Am 15.07.21 um 21:05 schrieb Felix Kuehling:

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: f91142c62161 ("drm/ttm: nuke VM_MIXEDMAP on BO mappings v3") Suggested-by: Daniel Vetter daniel.vetter@intel.com Tested-by: Felix Kuehling Felix.Kuehling@amd.com Signed-off-by: Felix Kuehling Felix.Kuehling@amd.com

I've reviewed and pushed the patch to drm-misc-fixes.

Regards, Christian.

---

drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 9 +++++++++ 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c index b3404c43a911..9f952b7fc197 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c @@ -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); }