Re: [PATCH 08/10] amdgpu: add support for memory cgroups

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Evicted VRAM BOs bypass memory cgroup (memcg) accounting because TTM_PL_FLAG_MEMCG is explicitly cleared during eviction.
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commit 05e0eb5ded826da3ea51ec14b35acb22f46c4aaa
Author: Dave Airlie <airlied@redhat.com>

amdgpu: add support for memory cgroups

This adds support for adding a obj cgroup to a buffer object,
and passing in the placement flags to make sure it's accounted
properly.

[ ... ]

> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 8062b3d611574..1c8123c564ac1 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -155,11 +155,14 @@ static void amdgpu_evict_flags(struct ttm_buffer_object *bo,
>  			amdgpu_bo_placement_from_domain(abo, AMDGPU_GEM_DOMAIN_GTT |
>  							AMDGPU_GEM_DOMAIN_CPU);
>  		}
> +		for (int i = 0; i < abo->placement.num_placement; i++)
> +			abo->placements[i].flags &= ~TTM_PL_FLAG_MEMCG;

[Severity: High]
Does clearing TTM_PL_FLAG_MEMCG here allow an application to bypass memcg
limits?

If a container continually allocates VRAM BOs, older BOs will be evicted to
system memory. Because the TTM_PL_FLAG_MEMCG flag is explicitly removed from
the placement flags in amdgpu_evict_flags(), it appears that the system memory
pages allocated during this eviction will not be charged to the application's
memcg, potentially allowing unbounded host memory consumption.

>  		break;
>  	case TTM_PL_TT:
>  	case AMDGPU_PL_PREEMPT:
>  	default:
>  		amdgpu_bo_placement_from_domain(abo, AMDGPU_GEM_DOMAIN_CPU);
> +		abo->placements[0].flags &= ~TTM_PL_FLAG_MEMCG;

[Severity: High]
Does this similarly drop memcg accounting when evicting other memory types to
the CPU domain?

>  		break;
>  	}
>  	*placement = abo->placement;

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Sashiko AI review · https://sashiko.dev/#/patchset/20260706052330.1110909-1-airlied@gmail.com?part=8