linux-kernel - Re: [PATCH 5.16 0702/1039] drm/amdgpu: Dont inherit GEM object VMAs in child process

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Date:   Tue, 25 Jan 2022 08:26:20 +0100
From:   Christian König <christian.koenig@....com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Felix Kuehling <Felix.Kuehling@....com>,
        David Yat Sin <david.yatsin@....com>,
        Rajneesh Bhardwaj <rajneesh.bhardwaj@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.16 0702/1039] drm/amdgpu: Dont inherit GEM object VMAs
 in child process

Hi Greg,

Am 24.01.22 um 19:41 schrieb Greg Kroah-Hartman:
> From: Rajneesh Bhardwaj <rajneesh.bhardwaj@....com>
>
> [ Upstream commit fbcdbfde87509d523132b59f661a355c731139d0 ]
>
> When an application having open file access to a node forks, its shared
> mappings also get reflected in the address space of child process even
> though it cannot access them with the object permissions applied. With the
> existing permission checks on the gem objects, it might be reasonable to
> also create the VMAs with VM_DONTCOPY flag so a user space application
> doesn't need to explicitly call the madvise(addr, len, MADV_DONTFORK)
> system call to prevent the pages in the mapped range to appear in the
> address space of the child process. It also prevents the memory leaks
> due to additional reference counts on the mapped BOs in the child
> process that prevented freeing the memory in the parent for which we had
> worked around earlier in the user space inside the thunk library.
>
> Additionally, we faced this issue when using CRIU to checkpoint restore
> an application that had such inherited mappings in the child which
> confuse CRIU when it mmaps on restore. Having this flag set for the
> render node VMAs helps. VMAs mapped via KFD already take care of this so
> this is needed only for the render nodes.
>
> To limit the impact of the change to user space consumers such as OpenGL
> etc, limit it to KFD BOs only.
>
> Acked-by: Felix Kuehling <Felix.Kuehling@....com>
> Reviewed-by: Christian König <christian.koenig@....com>
> Signed-off-by: David Yat Sin <david.yatsin@....com>
> Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@....com>
> Signed-off-by: Alex Deucher <alexander.deucher@....com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

Please drop this patch from all stable versions since it was reverted 
from upstream later on.

Regards,
Christian.

> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> index a1e63ba4c54a5..630dc99e49086 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> @@ -264,6 +264,9 @@ static int amdgpu_gem_object_mmap(struct drm_gem_object *obj, struct vm_area_str
>   	    !(vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)))
>   		vma->vm_flags &= ~VM_MAYWRITE;
>   
> +	if (bo->kfd_bo)
> +		vma->vm_flags |= VM_DONTCOPY;
> +
>   	return drm_gem_ttm_mmap(obj, vma);
>   }
>