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Subject: Re: [PATCH] drm/amdgpu: fix an underflow on non-4KB-page systems
To:     =?UTF-8?B?WOKEuSBSdW95YW8=?= <xry111@mengyan1223.wang>,
        Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
Cc:     David Airlie <airlied@linux.ie>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        =?UTF-8?Q?Dan_Hor=c3=a1k?= <dan@danny.cz>,
        amd-gfx@lists.freedesktop.org, Daniel Vetter <daniel@ffwll.ch>,
        stable@vger.kernel.org
References: <20210329175348.26859-1-xry111@mengyan1223.wang>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <ckoenig.leichtzumerken@gmail.com>
Message-ID: <d192e2a8-8baf-0a8c-93a9-9abbad992c7d@gmail.com>
Date:   Mon, 29 Mar 2021 20:04:00 +0200
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Am 29.03.21 um 19:53 schrieb Xℹ Ruoyao:
> If the initial value of `num_entires` (calculated at line 1654) is not
> an integral multiple of `AMDGPU_GPU_PAGES_IN_CPU_PAGE`, in line 1681 a
> value greater than the initial value will be assigned to it.  That causes
> `start > last + 1` after line 1708.  Then in the next iteration an
> underflow happens at line 1654.  It causes message
>
>      *ERROR* Couldn't update BO_VA (-12)
>
> printed in kernel log, and GPU hanging.
>
> Fortify the criteria of the loop to fix this issue.

NAK the value of num_entries must always be a multiple of 
AMDGPU_GPU_PAGES_IN_CPU_PAGE or otherwise we corrupt the page tables.

How do you trigger that?

Christian.

>
> BugLink: https://gitlab.freedesktop.org/drm/amd/-/issues/1549
> Fixes: a39f2a8d7066 ("drm/amdgpu: nuke amdgpu_vm_bo_split_mapping v2")
> Reported-by: Xi Ruoyao <xry111@mengyan1223.wang>
> Reported-by: Dan Horák <dan@danny.cz>
> Cc: stable@vger.kernel.org
> Signed-off-by: Xi Ruoyao <xry111@mengyan1223.wang>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> index ad91c0c3c423..cee0cc9c8085 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> @@ -1707,7 +1707,7 @@ static int amdgpu_vm_bo_update_mapping(struct amdgpu_device *adev,
>   		}
>   		start = tmp;
>   
> -	} while (unlikely(start != last + 1));
> +	} while (unlikely(start < last + 1));
>   
>   	r = vm->update_funcs->commit(&params, fence);
>   
>
> base-commit: a5e13c6df0e41702d2b2c77c8ad41677ebb065b3