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drm/amdgpu: workaround failed COW checks for Thunk VMAs

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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: f91142c621 ("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>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210715190537.585456-1-Felix.Kuehling@amd.com
Signed-off-by: Christian König <christian.koenig@amd.com>
This commit is contained in:
Felix Kuehling 2021-07-15 15:05:37 -04:00 committed by Christian König
parent 32a19de21a
commit fa5239f2af
1 changed files with 9 additions and 0 deletions
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9
drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
View file

@ -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);
}