Re: [PATCH] drm/amdgpu: add fast-path for userptr BO validation

["Christian König" <christian.koenig@amd.com>]

On 3/31/26 10:33, Wang, Beyond wrote:
> [Public]
> 
> This change is based on Linux 6.19-rc7
> 
> 
> Skip the expensive per-BO hmm_range_fault page table walk if no MMU
> invalidation occurred since last successful submit. Here it's a single
> seq counter compare vs the full HMM walk
> 
> On first submit the slow path runs and caches notifier_seq into
> bo->last_valid_notifier_seq. Subsequent submits check with the cached seq
> for the fast-path. If an MMU notifier fires, the seq changes accordingly
> and the slow path runs again on affected BOs.

Well absolutely clear NAK on that, we have intentionally removed that before because it leads to security issues.

Regards,
Christian.

> 
> Signed-off-by: Wang, Beyond <Wang.Beyond@amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c     | 25 +++++++++++++++++++++-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_object.h |  8 +++++++
>  2 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> index ecdfe6cb36cc..140346e9cb92 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> @@ -891,6 +891,17 @@ static int amdgpu_cs_parser_bos(struct amdgpu_cs_parser *p,
>                 bool userpage_invalidated = false;
>                 struct amdgpu_bo *bo = e->bo;
> 
> +               /*
> +                * Skip the expensive HMM page table walk if no MMU invalidation occurred
> +                * since last successful submit
> +                */
> +               if (bo->last_valid_notifier_seq &&
> +                   !mmu_interval_read_retry(&bo->notifier, bo->last_valid_notifier_seq)) {
> +                       e->range = NULL;
> +                       e->user_invalidated = false;
> +                       continue;
> +               }
> +
>                 e->range = amdgpu_hmm_range_alloc(NULL);
>                 if (unlikely(!e->range))
>                         return -ENOMEM;
> @@ -1326,7 +1337,19 @@ static int amdgpu_cs_submit(struct amdgpu_cs_parser *p,
>          */
>         r = 0;
>         amdgpu_bo_list_for_each_userptr_entry(e, p->bo_list) {
> -               r |= !amdgpu_hmm_range_valid(e->range);
> +               struct amdgpu_bo *bo = e->bo;
> +
> +               if (!e->range) {
> +                       if (mmu_interval_read_retry(&bo->notifier, bo->last_valid_notifier_seq))
> +                               r = 1;
> +                       continue;
> +               }
> +
> +               if (!amdgpu_hmm_range_valid(e->range))
> +                       r = 1;
> +               else
> +                       bo->last_valid_notifier_seq = e->range->hmm_range.notifier_seq;
> +
>                 amdgpu_hmm_range_free(e->range);
>                 e->range = NULL;
>         }
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
> index 52c2d1731aab..89dc9ee1176e 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
> @@ -115,6 +115,14 @@ struct amdgpu_bo {
> 
>  #ifdef CONFIG_MMU_NOTIFIER
>         struct mmu_interval_notifier    notifier;
> +
> +       /*
> +        * Cached notifier_seq from last successful CS submit.
> +        * Used to skip the expensive HMM page table walk when
> +        * no MMU invalidation has occurred since last validation.
> +        * Zero means never validated (always takes the slow path).
> +        */
> +       unsigned long                   last_valid_notifier_seq;
>  #endif
>         struct kgd_mem                  *kfd_bo;
> 
> --
> 2.43.0
> 
> 
> 
> Thanks,
> Beyond