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