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

[Christian König]

Am 08.07.21 um 21:36 schrieb Alex Deucher:
> 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.

I'm pretty sure that this is not working as expected.

>
> 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))

is_cow_mapping() already checks for VM_MAYWRITE, so this here shouldn't 
be necessary.

Christian.

>   		return -EINVAL;
>   
>   	ttm_bo_get(bo);