[PATCH 2/2] drm/ttm: Fix COW check

Alex Deucher alexander.deucher at amd.com
Thu Jul 8 19:36:21 UTC 2021

From: Felix Kuehling <Felix.Kuehling at amd.com>

KFD Thunk maps invisible VRAM BOs with PROT_NONE, MAP_PRIVATE.
is_cow_mapping returns true for these mappings. Add a check for
vm_flags & VM_WRITE to avoid mmap failures on private read-only or
PROT_NONE mappings.

Fixes: f91142c62161 ("drm/ttm: nuke VM_MIXEDMAP on BO mappings v3")
Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
drivers/gpu/drm/ttm/ttm_bo_vm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index f56be5bc0861..a75e90c7d4aa 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -552,7 +552,7 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
 int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
 	/* Enforce no COW since would have really strange behavior with it. */
-	if (is_cow_mapping(vma->vm_flags))
+	if (is_cow_mapping(vma->vm_flags) && (vma->vm_flags & VM_WRITE))
 		return -EINVAL;

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