On 12/17/20 3:10 PM, Christian König wrote:
[SNIP]
By eliminating such users, and replacing them with local maps which
are strictly bound in how long they can exist (and hence we can serialize against them finishing in our hotunplug code).
Not sure I see how serializing against BO map/unmap helps - our problem as you described is that once device is extracted and then something else quickly takes it's place in the PCI topology and gets assigned same physical IO ranges, then our driver will start accessing this new device because our 'zombie' BOs are still pointing to those ranges.
Until your driver's remove callback is finished the ranges stay reserved.
The ranges stay reserved until unmapped which happens in bo->destroy
I'm not sure of that. Why do you think that?
Because of this sequence ttm_bo_release->destroy->amdgpu_bo_destroy->amdgpu_bo_kunmap->...->iounmap Is there another place I am missing ?
which for most internally allocated buffers is during sw_fini when last drm_put is called.
If that's not the case, then hotunplug would be fundamentally impossible ot handle correctly.
Of course all the mmio actions will time out, so it might take some time to get through it all.
I found that PCI code provides pci_device_is_present function we can use to avoid timeouts - it reads device vendor and checks if all 1s is returned or not. We can call it from within register accessors before trying read/write
That's way to much overhead! We need to keep that much lower or it will result in quite a performance drop.
I suggest to rather think about adding drm_dev_enter/exit guards.
Sure, this one is just a bit upstream to the disconnect event. Eventually none of them is watertight.
Andrey
Christian.
Another point regarding serializing - problem is that some of those BOs are very long lived, take for example the HW command ring buffer Christian mentioned before - (amdgpu_ring_init->amdgpu_bo_create_kernel), it's life span is basically for the entire time the device exists, it's destroyed only in the SW fini stage (when last drm_dev reference is dropped) and so should I grab it's dma_resv_lock from amdgpu_pci_remove code and wait for it to be unmapped before proceeding with the PCI remove code ? This can take unbound time and that why I don't understand how serializing will help.
Uh you need to untangle that. After hw cleanup is done no one is allowed to touch that ringbuffer bo anymore from the kernel.
I would assume we are not allowed to touch it once we identified the device is gone in order to minimize the chance of accidental writes to some other device which might now occupy those IO ranges ?
That's what drm_dev_enter/exit guards are for. Like you say we cant wait for all sw references to disappear.
Yes, didn't make sense to me why would we use vmap_local for internally allocated buffers. I think we should also guard registers read/writes for the same reason as above.
The vmap_local is for mappings done by other drivers, through the dma-buf interface (where "other drivers" can include fbdev/fbcon, if you use the generic helpers). -Daniel
Ok, so I assumed that with vmap_local you were trying to solve the problem of quick reinsertion of another device into same MMIO range that my driver still points too but actually are you trying to solve the issue of exported dma buffers outliving the device ? For this we have drm_device refcount in the GEM layer i think.
Andrey
Andrey
It doesn't solve all your problems, but it's a tool to get there. -Daniel
Andrey
> - handle fbcon somehow. I think shutting it all down should work out. > - worst case keep the system backing storage around for shared dma-buf > until the other non-dynamic driver releases it. for vram we require > dynamic importers (and maybe it wasn't such a bright idea to allow > pinning of importer buffers, might need to revisit that). > > Cheers, Daniel > >> Christian. >> >>> Andrey >>> >>> >>>> -Daniel >>>> >>>>> Christian. >>>>> >>>>>> I loaded the driver with vm_update_mode=3 >>>>>> meaning all VM updates done using CPU and hasn't seen any OOPs after >>>>>> removing the device. I guess i can test it more by allocating GTT and >>>>>> VRAM BOs >>>>>> and trying to read/write to them after device is removed. >>>>>> >>>>>> Andrey >>>>>> >>>>>> >>>>>>> Regards, >>>>>>> Christian. >>>>>>> >>>>>>>> Andrey >>>>>> _______________________________________________ >>>>>> amd-gfx mailing list >>>>>> amd-gfx@lists.freedesktop.org >>>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.free... >>>>>> >>>>>>