Re: [PATCH 1/5] drm/xe: Guard against NULL GT in xe_sriov_vf.c

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

On 9/26/2025 5:59 PM, Jonathan Cavitt wrote:
> Static analysis reveals the following issue:
> xe_device_get_gt is theoretically able to return NULL in some cases, but
> several use cases don't check the return value before performing a
> dereference, resulting in a NULL pointer dereference.
> 
> Add guards against this in xe_sriov_vf.c:
> - Use xe_root_mmio_gt instead of xe_device_get_gt for the tile 0 case.
> - Check the return value of xe_device_get_gt when this is not possible.
> 
> Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_sriov_vf.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_sriov_vf.c b/drivers/gpu/drm/xe/xe_sriov_vf.c
> index cdd9f8e78b2a..28b9c40d79f0 100644
> --- a/drivers/gpu/drm/xe/xe_sriov_vf.c
> +++ b/drivers/gpu/drm/xe/xe_sriov_vf.c
> @@ -178,7 +178,7 @@ static void vf_migration_init_early(struct xe_device *xe)
>  	if (!IS_DGFX(xe)) {
>  		struct xe_uc_fw_version guc_version;
>  
> -		xe_gt_sriov_vf_guc_versions(xe_device_get_gt(xe, 0), NULL, &guc_version);
> +		xe_gt_sriov_vf_guc_versions(xe_root_mmio_gt(xe), NULL, &guc_version);
>  		if (MAKE_GUC_VER_STRUCT(guc_version) < MAKE_GUC_VER(1, 23, 0))
>  			return vf_disable_migration(xe,
>  						    "CCS migration requires GuC ABI >= 1.23 but only %u.%u found",
> @@ -361,6 +361,11 @@ static void vf_post_migration_recovery(struct xe_device *xe)
>  	while (id = vf_get_next_migrated_gt_id(xe), id >= 0) {
>  		struct xe_gt *gt = xe_device_get_gt(xe, id);
>  

I'm not sure this can ever fail, as ID it taken from vf_get_next_migrated_gt_id()
which uses the for_each_gt loop, so all IDs are taken from existing GTs, there is no guess

maybe just assert here?

> +		if (!gt) {
> +			err = -ENODEV;
> +			goto fail;
> +		}
> +
>  		err = gt_vf_post_migration_fixups(gt);
>  		if (err)
>  			goto fail;