[Intel-gfx] [PATCH] drm/i915/gem: Atomically invalidate userptr on mmu-notifier

[Andi Shyti]

Hi Jonathan,

On Tue, Nov 28, 2023 at 08:25:05AM -0800, Jonathan Cavitt wrote:
> Never block for outstanding work on userptr object upon receipt of a
> mmu-notifier. The reason we originally did so was to immediately unbind
> the userptr and unpin its pages, but since that has been dropped in
> commit b4b9731b02c3c ("drm/i915: Simplify userptr locking"), we never
> return the pages to the system i.e. never drop our page->mapcount and so
> do not allow the page and CPU PTE to be revoked. Based on this history,
> we know we are safe to drop the wait entirely.
> 
> Upon return from mmu-notifier, we will still have the userptr pages
> pinned preventing the following PTE operation (such as try_to_unmap)
> adjusting the vm_area_struct, so it is safe to keep the pages around for
> as long as we still have i/o pending.
> 
> We do not have any means currently to asynchronously revalidate the
> userptr pages, that is always prior to next use.
> 
> Signed-off-by: Chris Wilson <chris.p.wilson at linux.intel.com>
> Signed-off-by: Jonathan Cavitt <jonathan.cavitt at intel.com>

Reviewed-by: Andi Shyti <andi.shyti at linux.intel.com>

Thanks,
Andi