Am 24.11.20 um 17:22 schrieb Andrey Grodzovsky:
On 11/24/20 2:41 AM, Christian König wrote:
Am 23.11.20 um 22:08 schrieb Andrey Grodzovsky:
On 11/23/20 3:41 PM, Christian König wrote:
Am 23.11.20 um 21:38 schrieb Andrey Grodzovsky:
On 11/23/20 3:20 PM, Christian König wrote:
Am 23.11.20 um 21:05 schrieb Andrey Grodzovsky:
On 11/25/20 5:42 AM, Christian König wrote:
Am 21.11.20 um 06:21 schrieb Andrey Grodzovsky:
It's needed to drop iommu backed pages on device unplug
before device's IOMMU group is released.
It would be cleaner if we could do the whole handling in TTM. I
also need to double check what you are doing with this function.
Christian.
Check patch "drm/amdgpu: Register IOMMU topology notifier per
device." to see
how i use it. I don't see why this should go into TTM mid-layer
- the stuff I do inside
is vendor specific and also I don't think TTM is explicitly
aware of IOMMU ?
Do you mean you prefer the IOMMU notifier to be registered from
within TTM
and then use a hook to call into vendor specific handler ?
No, that is really vendor specific.
What I meant is to have a function like
ttm_resource_manager_evict_all() which you only need to call and
all tt objects are unpopulated.
So instead of this BO list i create and later iterate in amdgpu
from the IOMMU patch you just want to do it within
TTM with a single function ? Makes much more sense.
Yes, exactly.
The list_empty() checks we have in TTM for the LRU are actually not
the best idea, we should now check the pin_count instead. This way
we could also have a list of the pinned BOs in TTM.
So from my IOMMU topology handler I will iterate the TTM LRU for the
unpinned BOs and this new function for the pinned ones ?
It's probably a good idea to combine both iterations into this new
function to cover all the BOs allocated on the device.
Yes, that's what I had in my mind as well.
BTW: Have you thought about what happens when we unpopulate a BO
while we still try to use a kernel mapping for it? That could have
unforeseen consequences.
Are you asking what happens to kmap or vmap style mapped CPU
accesses once we drop all the DMA backing pages for a particular BO
? Because for user mappings
(mmap) we took care of this with dummy page reroute but indeed
nothing was done for in kernel CPU mappings.
Yes exactly that.
In other words what happens if we free the ring buffer while the
kernel still writes to it?
Christian.
While we can't control user application accesses to the mapped buffers
explicitly and hence we use page fault rerouting
I am thinking that in this case we may be able to sprinkle
drm_dev_enter/exit in any such sensitive place were we might
CPU access a DMA buffer from the kernel ?
Yes, I fear we are going to need that.
Things like CPU page table updates, ring buffer accesses and FW memcpy
? Is there other places ?
Puh, good question. I have no idea.
Another point is that at this point the driver shouldn't access any
such buffers as we are at the process finishing the device.
AFAIK there is no page fault mechanism for kernel mappings so I don't
think there is anything else to do ?
Well there is a page fault handler for kernel mappings, but that one
just prints the stack trace into the system log and calls BUG(); :)
Long story short we need to avoid any access to released pages after
unplug. No matter if it's from the kernel or userspace.
Regards,
Christian.
Andrey
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