Commit fa5239f2 authored by Felix Kuehling's avatar Felix Kuehling Committed by Christian König
Browse files

drm/amdgpu: workaround failed COW checks for Thunk VMAs 



KFD Thunk maps invisible VRAM BOs with PROT_NONE, MAP_PRIVATE.
is_cow_mapping returns true for these mappings, which causes mmap to fail
in ttm_bo_mmap_obj.

As a workaround, clear VM_MAYWRITE for PROT_NONE-COW mappings. This
should prevent the mapping from ever becoming writable and makes
is_cow_mapping(vm_flags) false.

Fixes: f91142c6 ("drm/ttm: nuke VM_MIXEDMAP on BO mappings v3")
Suggested-by: default avatarDaniel Vetter <daniel.vetter@intel.com>
Tested-by: default avatarFelix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: default avatarFelix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210715190537.585456-1-Felix.Kuehling@amd.com


Signed-off-by: default avatarChristian König <christian.koenig@amd.com>
parent 32a19de2

drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c

+9 −0
Original line number Diff line number Diff line
@@ -255,6 +255,15 @@ static int amdgpu_gem_object_mmap(struct drm_gem_object *obj, struct vm_area_str 
	if (bo->flags & AMDGPU_GEM_CREATE_NO_CPU_ACCESS)

		return -EPERM;



	/* Workaround for Thunk bug creating PROT_NONE,MAP_PRIVATE mappings

	 * for debugger access to invisible VRAM. Should have used MAP_SHARED

	 * instead. Clearing VM_MAYWRITE prevents the mapping from ever

	 * becoming writable and makes is_cow_mapping(vm_flags) false.

	 */

	if (is_cow_mapping(vma->vm_flags) &&

	    !(vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)))

		vma->vm_flags &= ~VM_MAYWRITE;



	return drm_gem_ttm_mmap(obj, vma);

}