[Patch v2] drm/amdgpu: Don't inherit GEM object VMAs in child process

[Felix Kuehling]

On 2021-12-10 4:48 p.m., Rajneesh Bhardwaj wrote:
> 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.
>
> Cc: Felix Kuehling <Felix.Kuehling at amd.com>
>
> Signed-off-by: David Yat Sin <david.yatsin at amd.com>
> Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj at amd.com>

Acked-by: Felix Kuehling <Felix.Kuehling at amd.com>


> ---
>
> Changes in v2:
>   * Addressed Christian's concerns for user space impact
>   * Further reduced the scope to KFD BOs only
>
>   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 a224b5295edd..64a7931eda8c 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> @@ -263,6 +263,9 @@ 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);
>   }
>