linux-kernel - Re: [PATCH] drm/amdgpu: Fix a potential sdma invalid access

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Date:   Fri, 2 Apr 2021 18:25:41 +0200
From:   Christian König <christian.koenig@....com>
To:     Qu Huang <jinsdb@....com>, alexander.deucher@....com,
        airlied@...ux.ie, daniel@...ll.ch, sumit.semwal@...aro.org,
        airlied@...hat.com, ray.huang@....com, Mihir.Patel@....com,
        nirmoy.aiemd@...il.com
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH] drm/amdgpu: Fix a potential sdma invalid access

Hi Qu,

Am 02.04.21 um 05:18 schrieb Qu Huang:
> Before dma_resv_lock(bo->base.resv, NULL) in amdgpu_bo_release_notify(),
> the bo->base.resv lock may be held by ttm_mem_evict_first(),

That can't happen since when bo_release_notify is called the BO has not 
more references and is therefore deleted.

And we never evict a deleted BO, we just wait for it to become idle.

Regards,
Christian.

> and the VRAM mem will be evicted, mem region was replaced
> by Gtt mem region. amdgpu_bo_release_notify() will then
> hold the bo->base.resv lock, and SDMA will get an invalid
> address in amdgpu_fill_buffer(), resulting in a VMFAULT
> or memory corruption.
>
> To avoid it, we have to hold bo->base.resv lock first, and
> check whether the mem.mem_type is TTM_PL_VRAM.
>
> Signed-off-by: Qu Huang <jinsdb@....com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> index 4b29b82..8018574 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> @@ -1300,12 +1300,16 @@ void amdgpu_bo_release_notify(struct ttm_buffer_object *bo)
>   	if (bo->base.resv == &bo->base._resv)
>   		amdgpu_amdkfd_remove_fence_on_pt_pd_bos(abo);
>
> -	if (bo->mem.mem_type != TTM_PL_VRAM || !bo->mem.mm_node ||
> -	    !(abo->flags & AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE))
> +	if (!(abo->flags & AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE))
>   		return;
>
>   	dma_resv_lock(bo->base.resv, NULL);
>
> +	if (bo->mem.mem_type != TTM_PL_VRAM || !bo->mem.mm_node) {
> +		dma_resv_unlock(bo->base.resv);
> +		return;
> +	}
> +
>   	r = amdgpu_fill_buffer(abo, AMDGPU_POISON, bo->base.resv, &fence);
>   	if (!WARN_ON(r)) {
>   		amdgpu_bo_fence(abo, fence, false);
> --
> 1.8.3.1
>