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@xxxxxxxxx>
Tested-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Signed-off-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
---
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);
}
--
2.32.0
