Re: [PATCH 1/3] drm/xe: Disable compression on SVM

[Matthew Auld <matthew.auld@intel.com>]

On 14/07/2025 18:33, Matthew Brost wrote:
> This is not yet supported, forcefully disable by setting pat_index to
> zero for CPU address mirror VMAs.
> 
> Cc: stable@vger.kernel.org
> Fixes: b43e864af0d4 ("drm/xe/uapi: Add DRM_XE_VM_BIND_FLAG_CPU_ADDR_MIRROR")
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_vm.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 2035604121e6..73cb981c0956 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -2362,7 +2362,10 @@ vm_bind_ioctl_ops_create(struct xe_vm *vm, struct xe_vma_ops *vops,
>   			op->map.is_cpu_addr_mirror = flags &
>   				DRM_XE_VM_BIND_FLAG_CPU_ADDR_MIRROR;
>   			op->map.dumpable = flags & DRM_XE_VM_BIND_FLAG_DUMPABLE;
> -			op->map.pat_index = pat_index;
> +			if (op->map.is_cpu_addr_mirror)
> +				op->map.pat_index = 0;

Is this meant as a safe default or is this just a dummy value? If this 
actually gets programmed in the hw, maybe XE_CACHE_WB would be better 
here? That way we know exactly what it does from driver POV for a given 
platform. Index zero for example might have no host coherency (might 
then need WC on host). In some world index zero could enable compression.

> +			else
> +				op->map.pat_index = pat_index;
>   			op->map.invalidate_on_bind =
>   				__xe_vm_needs_clear_scratch_pages(vm, flags);
>   		} else if (__op->op == DRM_GPUVA_OP_PREFETCH) {