Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" Andrey.Grodzovsky@amd.com:
On 6/5/20 2:40 PM, Christian König wrote:
Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky:
On 5/11/20 2:45 AM, Christian König wrote:
Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky:
Signed-off-by: Andrey Grodzovsky andrey.grodzovsky@amd.com
drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- include/drm/ttm/ttm_bo_driver.h | 2 ++ 2 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c index c5b516f..eae61cc 100644 --- a/drivers/gpu/drm/ttm/ttm_bo.c +++ b/drivers/gpu/drm/ttm/ttm_bo.c @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct ttm_buffer_object *bo) ttm_bo_unmap_virtual_locked(bo); ttm_mem_io_unlock(man); } +EXPORT_SYMBOL(ttm_bo_unmap_virtual); +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev) +{
- struct ttm_mem_type_manager *man;
- int i; -EXPORT_SYMBOL(ttm_bo_unmap_virtual);
- for (i = 0; i < TTM_NUM_MEM_TYPES; i++) {
man = &bdev->man[i];if (man->has_type && man->use_type)ttm_mem_io_lock(man, false);- }
You should drop that it will just result in a deadlock warning for Nouveau and has no effect at all.
Apart from that looks good to me, Christian.
As I am considering to re-include this in V2 of the patchsets, can you clarify please why this will have no effect at all ?
The locks are exclusive for Nouveau to allocate/free the io address space.
Since we don't do this here we don't need the locks.
Christian.
So basically calling unmap_mapping_range doesn't require any extra locking around it and whatever locks are taken within the function should be enough ?
I think so, yes.
Christian.
Andrey
Andrey
- unmap_mapping_range(bdev->dev_mapping, 0, 0 , 1);
- /*TODO What about ttm_mem_io_free_vm(bo) ? */
- for (i = TTM_NUM_MEM_TYPES - 1; i >= 0; i--) {
man = &bdev->man[i];if (man->has_type && man->use_type)ttm_mem_io_unlock(man);- }
+} +EXPORT_SYMBOL(ttm_bo_unmap_virtual_address_space); int ttm_bo_wait(struct ttm_buffer_object *bo, bool interruptible, bool no_wait) diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h index c9e0fd0..3133463 100644 --- a/include/drm/ttm/ttm_bo_driver.h +++ b/include/drm/ttm/ttm_bo_driver.h @@ -600,6 +600,8 @@ int ttm_bo_device_init(struct ttm_bo_device *bdev, */ void ttm_bo_unmap_virtual(struct ttm_buffer_object *bo); +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev);
- /**
- ttm_bo_unmap_virtual
On 6/9/20 7:21 PM, Koenig, Christian wrote:
Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" Andrey.Grodzovsky@amd.com:
On 6/5/20 2:40 PM, Christian König wrote: > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: >> >> On 5/11/20 2:45 AM, Christian König wrote: >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: >>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com> >>>> --- >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ >>>> 2 files changed, 23 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c >>>> b/drivers/gpu/drm/ttm/ttm_bo.c >>>> index c5b516f..eae61cc 100644 >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct >>>> ttm_buffer_object *bo) >>>> ttm_bo_unmap_virtual_locked(bo); >>>> ttm_mem_io_unlock(man); >>>> } >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>>> +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev) >>>> +{ >>>> + struct ttm_mem_type_manager *man; >>>> + int i; >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>> >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { >>>> + man = &bdev->man[i]; >>>> + if (man->has_type && man->use_type) >>>> + ttm_mem_io_lock(man, false); >>>> + } >>> >>> You should drop that it will just result in a deadlock warning for >>> Nouveau and has no effect at all. >>> >>> Apart from that looks good to me, >>> Christian. >> >> >> As I am considering to re-include this in V2 of the patchsets, can >> you clarify please why this will have no effect at all ? > > The locks are exclusive for Nouveau to allocate/free the io address > space. > > Since we don't do this here we don't need the locks. > > Christian. So basically calling unmap_mapping_range doesn't require any extra locking around it and whatever locks are taken within the function should be enough ?I think so, yes.
Christian.
Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running. So the device removed flag needs to be advertized before this function is run, (perhaps with a memory barrier pair). That should probably be added to the function documentation.
(Other than that, please add a commit message if respinning).
/Thomas
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote:
Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" Andrey.Grodzovsky@amd.com:
On 6/5/20 2:40 PM, Christian König wrote: > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: >> >> On 5/11/20 2:45 AM, Christian König wrote: >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: >>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com> >>>> --- >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ >>>> 2 files changed, 23 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c >>>> b/drivers/gpu/drm/ttm/ttm_bo.c >>>> index c5b516f..eae61cc 100644 >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct >>>> ttm_buffer_object *bo) >>>> ttm_bo_unmap_virtual_locked(bo); >>>> ttm_mem_io_unlock(man); >>>> } >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>>> +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev) >>>> +{ >>>> + struct ttm_mem_type_manager *man; >>>> + int i; >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>> >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { >>>> + man = &bdev->man[i]; >>>> + if (man->has_type && man->use_type) >>>> + ttm_mem_io_lock(man, false); >>>> + } >>> >>> You should drop that it will just result in a deadlock warning for >>> Nouveau and has no effect at all. >>> >>> Apart from that looks good to me, >>> Christian. >> >> >> As I am considering to re-include this in V2 of the patchsets, can >> you clarify please why this will have no effect at all ? > > The locks are exclusive for Nouveau to allocate/free the io address > space. > > Since we don't do this here we don't need the locks. > > Christian. So basically calling unmap_mapping_range doesn't require any extra locking around it and whatever locks are taken within the function should be enough ?I think so, yes.
Christian.
Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
So the device removed flag needs to be advertized before this function is run,
I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
Andrey
That should probably be added to the function documentation.
(Other than that, please add a commit message if respinning).
/Thomas
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote:
Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" Andrey.Grodzovsky@amd.com:
On 6/5/20 2:40 PM, Christian König wrote: > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: >> >> On 5/11/20 2:45 AM, Christian König wrote: >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: >>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com> >>>> --- >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ >>>> 2 files changed, 23 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c >>>> b/drivers/gpu/drm/ttm/ttm_bo.c >>>> index c5b516f..eae61cc 100644 >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct >>>> ttm_buffer_object *bo) >>>> ttm_bo_unmap_virtual_locked(bo); >>>> ttm_mem_io_unlock(man); >>>> } >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>>> +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev) >>>> +{ >>>> + struct ttm_mem_type_manager *man; >>>> + int i; >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>> >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { >>>> + man = &bdev->man[i]; >>>> + if (man->has_type && man->use_type) >>>> + ttm_mem_io_lock(man, false); >>>> + } >>> >>> You should drop that it will just result in a deadlock warning for >>> Nouveau and has no effect at all. >>> >>> Apart from that looks good to me, >>> Christian. >> >> >> As I am considering to re-include this in V2 of the patchsets, can >> you clarify please why this will have no effect at all ? > > The locks are exclusive for Nouveau to allocate/free the io address > space. > > Since we don't do this here we don't need the locks. > > Christian. So basically calling unmap_mapping_range doesn't require any extra locking around it and whatever locks are taken within the function should be enough ?I think so, yes.
Christian.
Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
So the device removed flag needs to be advertized before this function is run,
I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Christian.
Andrey
That should probably be added to the function documentation.
(Other than that, please add a commit message if respinning).
/Thomas
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote:
Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" Andrey.Grodzovsky@amd.com:
On 6/5/20 2:40 PM, Christian König wrote: > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: >> >> On 5/11/20 2:45 AM, Christian König wrote: >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: >>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com> >>>> --- >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ >>>> 2 files changed, 23 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c >>>> b/drivers/gpu/drm/ttm/ttm_bo.c >>>> index c5b516f..eae61cc 100644 >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct >>>> ttm_buffer_object *bo) >>>> ttm_bo_unmap_virtual_locked(bo); >>>> ttm_mem_io_unlock(man); >>>> } >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>>> +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev) >>>> +{ >>>> + struct ttm_mem_type_manager *man; >>>> + int i; >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>> >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { >>>> + man = &bdev->man[i]; >>>> + if (man->has_type && man->use_type) >>>> + ttm_mem_io_lock(man, false); >>>> + } >>> >>> You should drop that it will just result in a deadlock warning for >>> Nouveau and has no effect at all. >>> >>> Apart from that looks good to me, >>> Christian. >> >> >> As I am considering to re-include this in V2 of the patchsets, can >> you clarify please why this will have no effect at all ? > > The locks are exclusive for Nouveau to allocate/free the io address > space. > > Since we don't do this here we don't need the locks. > > Christian. So basically calling unmap_mapping_range doesn't require any extra locking around it and whatever locks are taken within the function should be enough ?I think so, yes.
Christian.
Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
So the device removed flag needs to be advertized before this function is run,
I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Christian.
Andrey
That should probably be added to the function documentation.
(Other than that, please add a commit message if respinning).
/Thomas
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote:
Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" Andrey.Grodzovsky@amd.com:
On 6/5/20 2:40 PM, Christian König wrote: > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: >> >> On 5/11/20 2:45 AM, Christian König wrote: >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: >>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com> >>>> --- >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ >>>> 2 files changed, 23 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c >>>> b/drivers/gpu/drm/ttm/ttm_bo.c >>>> index c5b516f..eae61cc 100644 >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct >>>> ttm_buffer_object *bo) >>>> ttm_bo_unmap_virtual_locked(bo); >>>> ttm_mem_io_unlock(man); >>>> } >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>>> +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev) >>>> +{ >>>> + struct ttm_mem_type_manager *man; >>>> + int i; >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>> >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { >>>> + man = &bdev->man[i]; >>>> + if (man->has_type && man->use_type) >>>> + ttm_mem_io_lock(man, false); >>>> + } >>> >>> You should drop that it will just result in a deadlock warning for >>> Nouveau and has no effect at all. >>> >>> Apart from that looks good to me, >>> Christian. >> >> >> As I am considering to re-include this in V2 of the patchsets, can >> you clarify please why this will have no effect at all ? > > The locks are exclusive for Nouveau to allocate/free the io address > space. > > Since we don't do this here we don't need the locks. > > Christian. So basically calling unmap_mapping_range doesn't require any extra locking around it and whatever locks are taken within the function should be enough ?I think so, yes.
Christian.
Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
So the device removed flag needs to be advertized before this function is run,
I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
For the special case of syncing a full address-space unmap_mapping_range() with fault handlers regardless of the reason for the full address-space unmap_mapping_range() one could either traverse the address space (drm_vma_manager) and grab *all* bo reservations around the unmap_mapping_range(), or grab the i_mmap_lock in read mode in the fault handler. (It's taken in write mode in unmap_mapping_range). While the latter may seem like a simple solution, one should probably consider the overhead both in run-time and scaling ability.
/Thomas
On Wed, Jun 10, 2020 at 10:30 PM Thomas Hellström (Intel) thomas_os@shipmail.org wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote:
Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" Andrey.Grodzovsky@amd.com:
On 6/5/20 2:40 PM, Christian König wrote: > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: >> >> On 5/11/20 2:45 AM, Christian König wrote: >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: >>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com> >>>> --- >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ >>>> 2 files changed, 23 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c >>>> b/drivers/gpu/drm/ttm/ttm_bo.c >>>> index c5b516f..eae61cc 100644 >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct >>>> ttm_buffer_object *bo) >>>> ttm_bo_unmap_virtual_locked(bo); >>>> ttm_mem_io_unlock(man); >>>> } >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>>> +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev) >>>> +{ >>>> + struct ttm_mem_type_manager *man; >>>> + int i; >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>> >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { >>>> + man = &bdev->man[i]; >>>> + if (man->has_type && man->use_type) >>>> + ttm_mem_io_lock(man, false); >>>> + } >>> >>> You should drop that it will just result in a deadlock warning for >>> Nouveau and has no effect at all. >>> >>> Apart from that looks good to me, >>> Christian. >> >> >> As I am considering to re-include this in V2 of the patchsets, can >> you clarify please why this will have no effect at all ? > > The locks are exclusive for Nouveau to allocate/free the io address > space. > > Since we don't do this here we don't need the locks. > > Christian. So basically calling unmap_mapping_range doesn't require any extra locking around it and whatever locks are taken within the function should be enough ?I think so, yes.
Christian.
Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
So the device removed flag needs to be advertized before this function is run,
I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
Hm ... Now I'm not sure drm_dev_enter/exit is actually good enough. I guess if you use vmf_insert_pfn within the drm_dev_enter/exit critical section, it should be fine. But I think you can also do fault handlers that just return the struct page and then let core handle the pte wrangling, those would indeed race and we can't have that I think.
I think we should try and make sure (as much as possible) that this is done all done in helpers and not some open coded stuff in drivers, or we'll just get it all wrong in the details.
For the special case of syncing a full address-space unmap_mapping_range() with fault handlers regardless of the reason for the full address-space unmap_mapping_range() one could either traverse the address space (drm_vma_manager) and grab *all* bo reservations around the unmap_mapping_range(), or grab the i_mmap_lock in read mode in the fault handler. (It's taken in write mode in unmap_mapping_range). While the latter may seem like a simple solution, one should probably consider the overhead both in run-time and scaling ability.
drm_dev_enter/exit uses srcu internally, so afaik should scale ridiculously well and be dirt cheap on the read side. It's horrible on the flush side in drm_dev_unplug, but hey no one cares about that :-) -Daniel
On 6/10/20 11:16 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 10:30 PM Thomas Hellström (Intel) thomas_os@shipmail.org wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote: > Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" > Andrey.Grodzovsky@amd.com: > > > On 6/5/20 2:40 PM, Christian König wrote: > > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: > >> > >> On 5/11/20 2:45 AM, Christian König wrote: > >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: > >>>> Signed-off-by: Andrey Grodzovsky andrey.grodzovsky@amd.com > >>>> --- > >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- > >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ > >>>> 2 files changed, 23 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c > >>>> b/drivers/gpu/drm/ttm/ttm_bo.c > >>>> index c5b516f..eae61cc 100644 > >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c > >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c > >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct > >>>> ttm_buffer_object *bo) > >>>> ttm_bo_unmap_virtual_locked(bo); > >>>> ttm_mem_io_unlock(man); > >>>> } > >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); > >>>> +void ttm_bo_unmap_virtual_address_space(struct > ttm_bo_device *bdev) > >>>> +{ > >>>> + struct ttm_mem_type_manager *man; > >>>> + int i; > >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); > >>> > >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { > >>>> + man = &bdev->man[i]; > >>>> + if (man->has_type && man->use_type) > >>>> + ttm_mem_io_lock(man, false); > >>>> + } > >>> > >>> You should drop that it will just result in a deadlock > warning for > >>> Nouveau and has no effect at all. > >>> > >>> Apart from that looks good to me, > >>> Christian. > >> > >> > >> As I am considering to re-include this in V2 of the > patchsets, can > >> you clarify please why this will have no effect at all ? > > > > The locks are exclusive for Nouveau to allocate/free the io > address > > space. > > > > Since we don't do this here we don't need the locks. > > > > Christian. > > > So basically calling unmap_mapping_range doesn't require any extra > locking around it and whatever locks are taken within the function > should be enough ? > > > > I think so, yes. > > Christian. Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
So the device removed flag needs to be advertized before this function is run,
I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
Hm ... Now I'm not sure drm_dev_enter/exit is actually good enough. I guess if you use vmf_insert_pfn within the drm_dev_enter/exit critical section, it should be fine. But I think you can also do fault handlers that just return the struct page and then let core handle the pte wrangling, those would indeed race and we can't have that I think.
For the TTM drivers, having a fault handler that defers the pte insertion to the core would break also the bo synchronization so I don't think that will ever happen. To make sure we could perhaps add a return value warning at the end of the fault handler with a comment explaining why this is a bad idea.
I think we should try and make sure (as much as possible) that this is done all done in helpers and not some open coded stuff in drivers, or we'll just get it all wrong in the details.
If doable, considering all the various fault handlers we have in DRM, I agree.
/Thomas
On Thu, Jun 11, 2020 at 08:12:37AM +0200, Thomas Hellström (Intel) wrote:
On 6/10/20 11:16 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 10:30 PM Thomas Hellström (Intel) thomas_os@shipmail.org wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote: > On 6/9/20 7:21 PM, Koenig, Christian wrote: > > Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" > > Andrey.Grodzovsky@amd.com: > > > > > > On 6/5/20 2:40 PM, Christian König wrote: > > > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: > > >> > > >> On 5/11/20 2:45 AM, Christian König wrote: > > >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: > > >>>> Signed-off-by: Andrey Grodzovsky andrey.grodzovsky@amd.com > > >>>> --- > > >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- > > >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ > > >>>> 2 files changed, 23 insertions(+), 1 deletion(-) > > >>>> > > >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c > > >>>> b/drivers/gpu/drm/ttm/ttm_bo.c > > >>>> index c5b516f..eae61cc 100644 > > >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c > > >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c > > >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct > > >>>> ttm_buffer_object *bo) > > >>>> ttm_bo_unmap_virtual_locked(bo); > > >>>> ttm_mem_io_unlock(man); > > >>>> } > > >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); > > >>>> +void ttm_bo_unmap_virtual_address_space(struct > > ttm_bo_device *bdev) > > >>>> +{ > > >>>> + struct ttm_mem_type_manager *man; > > >>>> + int i; > > >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); > > >>> > > >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { > > >>>> + man = &bdev->man[i]; > > >>>> + if (man->has_type && man->use_type) > > >>>> + ttm_mem_io_lock(man, false); > > >>>> + } > > >>> > > >>> You should drop that it will just result in a deadlock > > warning for > > >>> Nouveau and has no effect at all. > > >>> > > >>> Apart from that looks good to me, > > >>> Christian. > > >> > > >> > > >> As I am considering to re-include this in V2 of the > > patchsets, can > > >> you clarify please why this will have no effect at all ? > > > > > > The locks are exclusive for Nouveau to allocate/free the io > > address > > > space. > > > > > > Since we don't do this here we don't need the locks. > > > > > > Christian. > > > > > > So basically calling unmap_mapping_range doesn't require any extra > > locking around it and whatever locks are taken within the function > > should be enough ? > > > > > > > > I think so, yes. > > > > Christian. > Yes, that's true. However, without the bo reservation, nothing stops > a PTE from being immediately re-faulted back again. Even while > unmap_mapping_range() is running. > Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
> So the device removed flag needs to be advertized before this > function is run, > I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
> (perhaps with a memory barrier pair). > drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
Hm ... Now I'm not sure drm_dev_enter/exit is actually good enough. I guess if you use vmf_insert_pfn within the drm_dev_enter/exit critical section, it should be fine. But I think you can also do fault handlers that just return the struct page and then let core handle the pte wrangling, those would indeed race and we can't have that I think.
For the TTM drivers, having a fault handler that defers the pte insertion to the core would break also the bo synchronization so I don't think that will ever happen. To make sure we could perhaps add a return value warning at the end of the fault handler with a comment explaining why this is a bad idea.
Yeah good thing at least is that vram drivers all use ttm thus far, so that worry is handled.
And for usb/spi and other panels/ports connected over some bus that can't do mmio, the mmaps all point at system memory. So we don't have that problem there. -Daniel
I think we should try and make sure (as much as possible) that this is done all done in helpers and not some open coded stuff in drivers, or we'll just get it all wrong in the details.
If doable, considering all the various fault handlers we have in DRM, I agree.
/Thomas
On 6/10/20 5:16 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 10:30 PM Thomas Hellström (Intel) thomas_os@shipmail.org wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote: > Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" > Andrey.Grodzovsky@amd.com: > > > On 6/5/20 2:40 PM, Christian König wrote: > > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: > >> > >> On 5/11/20 2:45 AM, Christian König wrote: > >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: > >>>> Signed-off-by: Andrey Grodzovsky andrey.grodzovsky@amd.com > >>>> --- > >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- > >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ > >>>> 2 files changed, 23 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c > >>>> b/drivers/gpu/drm/ttm/ttm_bo.c > >>>> index c5b516f..eae61cc 100644 > >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c > >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c > >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct > >>>> ttm_buffer_object *bo) > >>>> ttm_bo_unmap_virtual_locked(bo); > >>>> ttm_mem_io_unlock(man); > >>>> } > >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); > >>>> +void ttm_bo_unmap_virtual_address_space(struct > ttm_bo_device *bdev) > >>>> +{ > >>>> + struct ttm_mem_type_manager *man; > >>>> + int i; > >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); > >>> > >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { > >>>> + man = &bdev->man[i]; > >>>> + if (man->has_type && man->use_type) > >>>> + ttm_mem_io_lock(man, false); > >>>> + } > >>> > >>> You should drop that it will just result in a deadlock > warning for > >>> Nouveau and has no effect at all. > >>> > >>> Apart from that looks good to me, > >>> Christian. > >> > >> > >> As I am considering to re-include this in V2 of the > patchsets, can > >> you clarify please why this will have no effect at all ? > > > > The locks are exclusive for Nouveau to allocate/free the io > address > > space. > > > > Since we don't do this here we don't need the locks. > > > > Christian. > > > So basically calling unmap_mapping_range doesn't require any extra > locking around it and whatever locks are taken within the function > should be enough ? > > > > I think so, yes. > > Christian. Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
So the device removed flag needs to be advertized before this function is run,
I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
Hm ... Now I'm not sure drm_dev_enter/exit is actually good enough. I guess if you use vmf_insert_pfn within the drm_dev_enter/exit critical section, it should be fine. But I think you can also do fault handlers that just return the struct page and then let core handle the pte wrangling, those would indeed race and we can't have that I think.
I think we should try and make sure (as much as possible) that this is done all done in helpers and not some open coded stuff in drivers, or we'll just get it all wrong in the details.
Can you please clarify this last paragraph ? Where in your opinion should I place the drm_dev_enter/exit and the zero page setting to faulting VA's PTEs ? I was planning to do it in amdgpu specific .fault handler which in turn calls to ttm_bo_vm_fault.
Andrey
For the special case of syncing a full address-space unmap_mapping_range() with fault handlers regardless of the reason for the full address-space unmap_mapping_range() one could either traverse the address space (drm_vma_manager) and grab *all* bo reservations around the unmap_mapping_range(), or grab the i_mmap_lock in read mode in the fault handler. (It's taken in write mode in unmap_mapping_range). While the latter may seem like a simple solution, one should probably consider the overhead both in run-time and scaling ability.
drm_dev_enter/exit uses srcu internally, so afaik should scale ridiculously well and be dirt cheap on the read side. It's horrible on the flush side in drm_dev_unplug, but hey no one cares about that :-) -Daniel
On Thu, Jun 11, 2020 at 11:15:42AM -0400, Andrey Grodzovsky wrote:
On 6/10/20 5:16 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 10:30 PM Thomas Hellström (Intel) thomas_os@shipmail.org wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote: > On 6/9/20 7:21 PM, Koenig, Christian wrote: > > Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" > > Andrey.Grodzovsky@amd.com: > > > > > > On 6/5/20 2:40 PM, Christian König wrote: > > > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: > > >> > > >> On 5/11/20 2:45 AM, Christian König wrote: > > >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: > > >>>> Signed-off-by: Andrey Grodzovsky andrey.grodzovsky@amd.com > > >>>> --- > > >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- > > >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ > > >>>> 2 files changed, 23 insertions(+), 1 deletion(-) > > >>>> > > >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c > > >>>> b/drivers/gpu/drm/ttm/ttm_bo.c > > >>>> index c5b516f..eae61cc 100644 > > >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c > > >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c > > >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct > > >>>> ttm_buffer_object *bo) > > >>>> ttm_bo_unmap_virtual_locked(bo); > > >>>> ttm_mem_io_unlock(man); > > >>>> } > > >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); > > >>>> +void ttm_bo_unmap_virtual_address_space(struct > > ttm_bo_device *bdev) > > >>>> +{ > > >>>> + struct ttm_mem_type_manager *man; > > >>>> + int i; > > >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); > > >>> > > >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { > > >>>> + man = &bdev->man[i]; > > >>>> + if (man->has_type && man->use_type) > > >>>> + ttm_mem_io_lock(man, false); > > >>>> + } > > >>> > > >>> You should drop that it will just result in a deadlock > > warning for > > >>> Nouveau and has no effect at all. > > >>> > > >>> Apart from that looks good to me, > > >>> Christian. > > >> > > >> > > >> As I am considering to re-include this in V2 of the > > patchsets, can > > >> you clarify please why this will have no effect at all ? > > > > > > The locks are exclusive for Nouveau to allocate/free the io > > address > > > space. > > > > > > Since we don't do this here we don't need the locks. > > > > > > Christian. > > > > > > So basically calling unmap_mapping_range doesn't require any extra > > locking around it and whatever locks are taken within the function > > should be enough ? > > > > > > > > I think so, yes. > > > > Christian. > Yes, that's true. However, without the bo reservation, nothing stops > a PTE from being immediately re-faulted back again. Even while > unmap_mapping_range() is running. > Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
> So the device removed flag needs to be advertized before this > function is run, > I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
> (perhaps with a memory barrier pair). > drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
Hm ... Now I'm not sure drm_dev_enter/exit is actually good enough. I guess if you use vmf_insert_pfn within the drm_dev_enter/exit critical section, it should be fine. But I think you can also do fault handlers that just return the struct page and then let core handle the pte wrangling, those would indeed race and we can't have that I think.
I think we should try and make sure (as much as possible) that this is done all done in helpers and not some open coded stuff in drivers, or we'll just get it all wrong in the details.
Can you please clarify this last paragraph ? Where in your opinion should I place the drm_dev_enter/exit and the zero page setting to faulting VA's PTEs ? I was planning to do it in amdgpu specific .fault handler which in turn calls to ttm_bo_vm_fault.
Nah, I think this should be done in ttm_bo_vm_fault. Reinventing this wheel in every driver is going to be horrible. Rough control flow:
if (!drm_dev_enter()) { /* insert dummy page pfn, the hw is gone */
return; }
/* old page fault handling code with vm_insert_pfn and all the * same locking as before */
drm_dev_exit();
Cheers, Daniel
Andrey
For the special case of syncing a full address-space unmap_mapping_range() with fault handlers regardless of the reason for the full address-space unmap_mapping_range() one could either traverse the address space (drm_vma_manager) and grab *all* bo reservations around the unmap_mapping_range(), or grab the i_mmap_lock in read mode in the fault handler. (It's taken in write mode in unmap_mapping_range). While the latter may seem like a simple solution, one should probably consider the overhead both in run-time and scaling ability.
drm_dev_enter/exit uses srcu internally, so afaik should scale ridiculously well and be dirt cheap on the read side. It's horrible on the flush side in drm_dev_unplug, but hey no one cares about that :-) -Daniel
On 6/10/20 4:30 PM, Thomas Hellström (Intel) wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote:
Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" Andrey.Grodzovsky@amd.com:
On 6/5/20 2:40 PM, Christian König wrote: > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: >> >> On 5/11/20 2:45 AM, Christian König wrote: >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: >>>> Signed-off-by: Andrey Grodzovsky andrey.grodzovsky@amd.com >>>> --- >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ >>>> 2 files changed, 23 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c >>>> b/drivers/gpu/drm/ttm/ttm_bo.c >>>> index c5b516f..eae61cc 100644 >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct >>>> ttm_buffer_object *bo) >>>> ttm_bo_unmap_virtual_locked(bo); >>>> ttm_mem_io_unlock(man); >>>> } >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>>> +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev) >>>> +{ >>>> + struct ttm_mem_type_manager *man; >>>> + int i; >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>> >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { >>>> + man = &bdev->man[i]; >>>> + if (man->has_type && man->use_type) >>>> + ttm_mem_io_lock(man, false); >>>> + } >>> >>> You should drop that it will just result in a deadlock warning for >>> Nouveau and has no effect at all. >>> >>> Apart from that looks good to me, >>> Christian. >> >> >> As I am considering to re-include this in V2 of the patchsets, can >> you clarify please why this will have no effect at all ? > > The locks are exclusive for Nouveau to allocate/free the io address > space. > > Since we don't do this here we don't need the locks. > > Christian.
So basically calling unmap_mapping_range doesn't require any extra locking around it and whatever locks are taken within the function should be enough ?
I think so, yes.
Christian.
Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
So the device removed flag needs to be advertized before this function is run,
I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
If you mean those fault handlers that were in progress when the flag (drm_dev_unplug) was set in amdgpu_pci_remove then as long as i wrap the entire fault handler (probably using amdgpu specific .fault hook around ttm_bo_vm_fault) with drm_dev_enter/exit pair then drm_dev_unplug->synchronize_srcu will block until those in progress faults have completed and only after this i will call unmap_mapping_range. Should this be enough ?
Andrey
For the special case of syncing a full address-space unmap_mapping_range() with fault handlers regardless of the reason for the full address-space unmap_mapping_range() one could either traverse the address space (drm_vma_manager) and grab *all* bo reservations around the unmap_mapping_range(), or grab the i_mmap_lock in read mode in the fault handler. (It's taken in write mode in unmap_mapping_range). While the latter may seem like a simple solution, one should probably consider the overhead both in run-time and scaling ability.
/Thomas
On 6/10/20 11:19 PM, Andrey Grodzovsky wrote:
On 6/10/20 4:30 PM, Thomas Hellström (Intel) wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote: > > Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" > Andrey.Grodzovsky@amd.com: > > > On 6/5/20 2:40 PM, Christian König wrote: > > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: > >> > >> On 5/11/20 2:45 AM, Christian König wrote: > >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: > >>>> Signed-off-by: Andrey Grodzovsky > andrey.grodzovsky@amd.com > >>>> --- > >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- > >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ > >>>> 2 files changed, 23 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c > >>>> b/drivers/gpu/drm/ttm/ttm_bo.c > >>>> index c5b516f..eae61cc 100644 > >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c > >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c > >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct > >>>> ttm_buffer_object *bo) > >>>> ttm_bo_unmap_virtual_locked(bo); > >>>> ttm_mem_io_unlock(man); > >>>> } > >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); > >>>> +void ttm_bo_unmap_virtual_address_space(struct > ttm_bo_device *bdev) > >>>> +{ > >>>> + struct ttm_mem_type_manager *man; > >>>> + int i; > >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); > >>> > >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { > >>>> + man = &bdev->man[i]; > >>>> + if (man->has_type && man->use_type) > >>>> + ttm_mem_io_lock(man, false); > >>>> + } > >>> > >>> You should drop that it will just result in a deadlock > warning for > >>> Nouveau and has no effect at all. > >>> > >>> Apart from that looks good to me, > >>> Christian. > >> > >> > >> As I am considering to re-include this in V2 of the > patchsets, can > >> you clarify please why this will have no effect at all ? > > > > The locks are exclusive for Nouveau to allocate/free the io > address > > space. > > > > Since we don't do this here we don't need the locks. > > > > Christian. > > > So basically calling unmap_mapping_range doesn't require > any extra > locking around it and whatever locks are taken within the > function > should be enough ? > > > > I think so, yes. > > Christian. Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
So the device removed flag needs to be advertized before this function is run,
I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
(perhaps with a memory barrier pair).
drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
If you mean those fault handlers that were in progress when the flag (drm_dev_unplug) was set in amdgpu_pci_remove then as long as i wrap the entire fault handler (probably using amdgpu specific .fault hook around ttm_bo_vm_fault) with drm_dev_enter/exit pair then drm_dev_unplug->synchronize_srcu will block until those in progress faults have completed and only after this i will call unmap_mapping_range. Should this be enough ?
Andrey
Yes, I believe so. Although I suspect you might trip lockdep with reverse locking order against the mmap_sem which is a constant pain in fault handlers. If that's the case, you might be able to introduce another srcu lock for this special purpose and synchronize just before the address-space-wide unmap_mapping_range(). If it turns out that an address space srcu lock like this is really needed, we should follow Daniel's suggestion and try to use it from drm-wide helpers.
/Thomas
On 6/11/20 2:35 AM, Thomas Hellström (Intel) wrote:
On 6/10/20 11:19 PM, Andrey Grodzovsky wrote:
On 6/10/20 4:30 PM, Thomas Hellström (Intel) wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote: > > On 6/9/20 7:21 PM, Koenig, Christian wrote: >> >> Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" >> Andrey.Grodzovsky@amd.com: >> >> >> On 6/5/20 2:40 PM, Christian König wrote: >> > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: >> >> >> >> On 5/11/20 2:45 AM, Christian König wrote: >> >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: >> >>>> Signed-off-by: Andrey Grodzovsky >> andrey.grodzovsky@amd.com >> >>>> --- >> >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- >> >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ >> >>>> 2 files changed, 23 insertions(+), 1 deletion(-) >> >>>> >> >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c >> >>>> b/drivers/gpu/drm/ttm/ttm_bo.c >> >>>> index c5b516f..eae61cc 100644 >> >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c >> >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c >> >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct >> >>>> ttm_buffer_object *bo) >> >>>> ttm_bo_unmap_virtual_locked(bo); >> >>>> ttm_mem_io_unlock(man); >> >>>> } >> >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); >> >>>> +void ttm_bo_unmap_virtual_address_space(struct >> ttm_bo_device *bdev) >> >>>> +{ >> >>>> + struct ttm_mem_type_manager *man; >> >>>> + int i; >> >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); >> >>> >> >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { >> >>>> + man = &bdev->man[i]; >> >>>> + if (man->has_type && man->use_type) >> >>>> + ttm_mem_io_lock(man, false); >> >>>> + } >> >>> >> >>> You should drop that it will just result in a deadlock >> warning for >> >>> Nouveau and has no effect at all. >> >>> >> >>> Apart from that looks good to me, >> >>> Christian. >> >> >> >> >> >> As I am considering to re-include this in V2 of the >> patchsets, can >> >> you clarify please why this will have no effect at all ? >> > >> > The locks are exclusive for Nouveau to allocate/free the io >> address >> > space. >> > >> > Since we don't do this here we don't need the locks. >> > >> > Christian. >> >> >> So basically calling unmap_mapping_range doesn't require >> any extra >> locking around it and whatever locks are taken within the >> function >> should be enough ? >> >> >> >> I think so, yes. >> >> Christian. > Yes, that's true. However, without the bo reservation, nothing > stops > a PTE from being immediately re-faulted back again. Even while > unmap_mapping_range() is running. > Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
> So the device removed flag needs to be advertized before this > function is run, > I indeed intend to call this right after calling drm_dev_unplug from amdgpu_pci_remove while adding drm_dev_enter/exit in ttm_bo_vm_fault (or in amdgpu specific wrapper since I don't see how can I access struct drm_device from ttm_bo_vm_fault) and this in my understanding should stop a PTE from being re-faulted back as you pointed out - so again I don't see how bo reservation would prevent it so it looks like I am missing something...
> (perhaps with a memory barrier pair). > drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I don't think require any extra memory barriers for visibility of the removed flag being set
As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
If you mean those fault handlers that were in progress when the flag (drm_dev_unplug) was set in amdgpu_pci_remove then as long as i wrap the entire fault handler (probably using amdgpu specific .fault hook around ttm_bo_vm_fault) with drm_dev_enter/exit pair then drm_dev_unplug->synchronize_srcu will block until those in progress faults have completed and only after this i will call unmap_mapping_range. Should this be enough ?
Andrey
Yes, I believe so. Although I suspect you might trip lockdep with reverse locking order against the mmap_sem which is a constant pain in fault handlers. If that's the case, you might be able to introduce another srcu lock for this special purpose and synchronize just before the address-space-wide unmap_mapping_range(). If it turns out that an address space srcu lock like this is really needed, we should follow Daniel's suggestion and try to use it from drm-wide helpers.
/Thomas
Does it make sense to prefault and set to zero page the entire VA range covered by the given VMA on the first page fault post device disconnect to save on other similar page faults ?
Andrey
On Thu, Jun 11, 2020 at 11:06:16AM -0400, Andrey Grodzovsky wrote:
On 6/11/20 2:35 AM, Thomas Hellström (Intel) wrote:
On 6/10/20 11:19 PM, Andrey Grodzovsky wrote:
On 6/10/20 4:30 PM, Thomas Hellström (Intel) wrote:
On 6/10/20 5:30 PM, Daniel Vetter wrote:
On Wed, Jun 10, 2020 at 04:05:04PM +0200, Christian König wrote:
Am 10.06.20 um 15:54 schrieb Andrey Grodzovsky: > > On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote: > > > > On 6/9/20 7:21 PM, Koenig, Christian wrote: > > > > > > Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" > > > Andrey.Grodzovsky@amd.com: > > > > > > > > > On 6/5/20 2:40 PM, Christian König wrote: > > > > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: > > > >> > > > >> On 5/11/20 2:45 AM, Christian König wrote: > > > >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: > > > >>>> Signed-off-by: Andrey Grodzovsky > > > andrey.grodzovsky@amd.com > > > >>>> --- > > > >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- > > > >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ > > > >>>> 2 files changed, 23 insertions(+), 1 deletion(-) > > > >>>> > > > >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c > > > >>>> b/drivers/gpu/drm/ttm/ttm_bo.c > > > >>>> index c5b516f..eae61cc 100644 > > > >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c > > > >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c > > > >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct > > > >>>> ttm_buffer_object *bo) > > > >>>> ttm_bo_unmap_virtual_locked(bo); > > > >>>> ttm_mem_io_unlock(man); > > > >>>> } > > > >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); > > > >>>> +void ttm_bo_unmap_virtual_address_space(struct > > > ttm_bo_device *bdev) > > > >>>> +{ > > > >>>> + struct ttm_mem_type_manager *man; > > > >>>> + int i; > > > >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); > > > >>> > > > >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { > > > >>>> + man = &bdev->man[i]; > > > >>>> + if (man->has_type && man->use_type) > > > >>>> + ttm_mem_io_lock(man, false); > > > >>>> + } > > > >>> > > > >>> You should drop that it will just result in a deadlock > > > warning for > > > >>> Nouveau and has no effect at all. > > > >>> > > > >>> Apart from that looks good to me, > > > >>> Christian. > > > >> > > > >> > > > >> As I am considering to re-include this in V2 of the > > > patchsets, can > > > >> you clarify please why this will have no effect at all ? > > > > > > > > The locks are exclusive for Nouveau to allocate/free the io > > > address > > > > space. > > > > > > > > Since we don't do this here we don't need the locks. > > > > > > > > Christian. > > > > > > > > > So basically calling > > > unmap_mapping_range doesn't require any > > > extra > > > locking around it and whatever locks > > > are taken within the function > > > should be enough ? > > > > > > > > > > > > I think so, yes. > > > > > > Christian. > > Yes, that's true. However, without the bo > > reservation, nothing stops > > a PTE from being immediately re-faulted back again. Even while > > unmap_mapping_range() is running. > > > Can you explain more on this - specifically, which > function to reserve > the BO, why BO reservation would prevent re-fault of the PTE ? > Thomas is talking about ttm_bo_reserver()/ttm_bo_unreserve(), but we don't need this because we unmap everything because the whole device is gone and not just manipulate a single BO.
> > So the device removed flag needs to be advertized before this > > function is run, > > > I indeed intend to call this right after calling > drm_dev_unplug from > amdgpu_pci_remove while adding drm_dev_enter/exit in > ttm_bo_vm_fault (or > in amdgpu specific wrapper since I don't see how can I access struct > drm_device from ttm_bo_vm_fault) and this in my understanding should > stop a PTE from being re-faulted back as you pointed > out - so again I > don't see how bo reservation would prevent it so it looks like I am > missing something... > > > > (perhaps with a memory barrier pair). > > > drm_dev_unplug and drm_dev_enter/exit are RCU synchronized and so I > don't think require any extra memory barriers for visibility of the > removed flag being set > As far as I can see that should be perfectly sufficient.
Only if you have a drm_dev_enter/exit pair in your fault handler. Otherwise you're still open to the races Thomas described. But aside from that the drm_dev_unplug stuff has all the barriers and stuff to make sure nothing escapes.
Failure to drm_dev_enter could then also trigger the special case where we put a dummy page in place. -Daniel
Hmm, Yes, indeed advertizing the flag before the call to unmap_mapping_range isn't enough, since there might be fault handlers running that haven't picked up the flag when unmap_mapping_range is launched.
If you mean those fault handlers that were in progress when the flag (drm_dev_unplug) was set in amdgpu_pci_remove then as long as i wrap the entire fault handler (probably using amdgpu specific .fault hook around ttm_bo_vm_fault) with drm_dev_enter/exit pair then drm_dev_unplug->synchronize_srcu will block until those in progress faults have completed and only after this i will call unmap_mapping_range. Should this be enough ?
Andrey
Yes, I believe so. Although I suspect you might trip lockdep with reverse locking order against the mmap_sem which is a constant pain in fault handlers. If that's the case, you might be able to introduce another srcu lock for this special purpose and synchronize just before the address-space-wide unmap_mapping_range(). If it turns out that an address space srcu lock like this is really needed, we should follow Daniel's suggestion and try to use it from drm-wide helpers.
/Thomas
Does it make sense to prefault and set to zero page the entire VA range covered by the given VMA on the first page fault post device disconnect to save on other similar page faults ?
Performance doesn't matter at all on hotunplug, as long as we eventually finish. Timing out the pci transactions will be so slow (while all the hotunplug processing is going on) that serving a few billion minor faults is peanuts. Simpler code wins here imo.
Also if you want to prefault, you also really want to prefault for the normal use-case, and that should be done (iirc already is?) in the ttm fault handler. -Daniel
Andrey
On 6/10/20 3:54 PM, Andrey Grodzovsky wrote:
On 6/10/20 6:15 AM, Thomas Hellström (Intel) wrote:
On 6/9/20 7:21 PM, Koenig, Christian wrote:
Am 09.06.2020 18:37 schrieb "Grodzovsky, Andrey" Andrey.Grodzovsky@amd.com:
On 6/5/20 2:40 PM, Christian König wrote: > Am 05.06.20 um 16:29 schrieb Andrey Grodzovsky: >> >> On 5/11/20 2:45 AM, Christian König wrote: >>> Am 09.05.20 um 20:51 schrieb Andrey Grodzovsky: >>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com> >>>> --- >>>> drivers/gpu/drm/ttm/ttm_bo.c | 22 +++++++++++++++++++++- >>>> include/drm/ttm/ttm_bo_driver.h | 2 ++ >>>> 2 files changed, 23 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c >>>> b/drivers/gpu/drm/ttm/ttm_bo.c >>>> index c5b516f..eae61cc 100644 >>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c >>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c >>>> @@ -1750,9 +1750,29 @@ void ttm_bo_unmap_virtual(struct >>>> ttm_buffer_object *bo) >>>> ttm_bo_unmap_virtual_locked(bo); >>>> ttm_mem_io_unlock(man); >>>> } >>>> +EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>>> +void ttm_bo_unmap_virtual_address_space(struct ttm_bo_device *bdev) >>>> +{ >>>> + struct ttm_mem_type_manager *man; >>>> + int i; >>>> -EXPORT_SYMBOL(ttm_bo_unmap_virtual); >>> >>>> + for (i = 0; i < TTM_NUM_MEM_TYPES; i++) { >>>> + man = &bdev->man[i]; >>>> + if (man->has_type && man->use_type) >>>> + ttm_mem_io_lock(man, false); >>>> + } >>> >>> You should drop that it will just result in a deadlock warning for >>> Nouveau and has no effect at all. >>> >>> Apart from that looks good to me, >>> Christian. >> >> >> As I am considering to re-include this in V2 of the patchsets, can >> you clarify please why this will have no effect at all ? > > The locks are exclusive for Nouveau to allocate/free the io address > space. > > Since we don't do this here we don't need the locks. > > Christian. So basically calling unmap_mapping_range doesn't require any extra locking around it and whatever locks are taken within the function should be enough ?I think so, yes.
Christian.
Yes, that's true. However, without the bo reservation, nothing stops a PTE from being immediately re-faulted back again. Even while unmap_mapping_range() is running.
Can you explain more on this - specifically, which function to reserve the BO, why BO reservation would prevent re-fault of the PTE ?
The bo reservation is taken in the TTM fault handler and temporarily blocks inserting a new PTE. So typically the bo reservation is held around unmap_mapping_range() and the buffer object operation that triggered it (typically a move or change of backing store).
/Thomas
dri-devel@lists.freedesktop.org
-
Andrey Grodzovsky -
Christian König -
Daniel Vetter -
Koenig, Christian
-
Thomas Hellström (Intel)