Re: [PATCH v2 5/5] drm/xe/vf: Use marker to catch fixups during LRC creation

[Matthew Brost <matthew.brost@intel.com>]

On Thu, Feb 19, 2026 at 12:21:58AM +0100, Tomasz Lis wrote:
> When LRC is created during fixups, it may have invalid state. Ensure
> that all such situations are caught, so that LRC creation can be
> repeated.
> 
> Due to VM having arbitrarly set amount of CPU cores, it is possible
> to limit the amount to 1. In such case, there is a possibility that
> kernel will switch CPU contexts in a way which makes previously used
> detection methods miss a VF migration recovery running in parallel
> (by simply not switching to the LRC creation thread during recovery).
> 
> This possibility is not only theoretical, it was revealed by testing
> that in a small percentage of specially crafted test cases, the
> resulting LRC is damaged and causes GPU hang.
> 
> With the additional atomic value increased after fixups, any VF
> migration that avoided the usual detection during LRC creation will
> be caught.
> 
> Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_exec_queue.c        | 6 +++++-
>  drivers/gpu/drm/xe/xe_gt_sriov_vf.c       | 7 +++++++
>  drivers/gpu/drm/xe/xe_gt_sriov_vf.h       | 1 +
>  drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h | 2 ++
>  4 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
> index 2ebf25a35557..a8d26fece38a 100644
> --- a/drivers/gpu/drm/xe/xe_exec_queue.c
> +++ b/drivers/gpu/drm/xe/xe_exec_queue.c
> @@ -308,15 +308,19 @@ static int __xe_exec_queue_init(struct xe_exec_queue *q, u32 exec_queue_flags)
>  	 */
>  	for (i = 0; i < q->width; ++i) {
>  		struct xe_lrc *lrc;
> +		int marker;
>  
>  		xe_gt_sriov_vf_wait_valid_default_lrc(q->gt);
> +		marker = xe_vf_migration_fixups_complete_count(q->gt);
> +
>  		lrc = xe_lrc_create(q->hwe, q->vm, q->replay_state,
>  				    xe_lrc_ring_size(), q->msix_vec, flags);
>  		if (IS_ERR(lrc)) {
>  			err = PTR_ERR(lrc);
>  			goto err_lrc;
>  		}
> -		if (!xe_gt_vf_valid_default_lrc(q->gt)) {
> +		if (!xe_gt_vf_valid_default_lrc(q->gt) ||
> +		    marker != xe_vf_migration_fixups_complete_count(q->gt)) {
>  			xe_lrc_put(lrc);

What exactly does this marker buy us? Couldn't patch #3 just signal
'gt->sriov.vf.migration.default_lrcs_need_fixes' where
'gt->sriov.vf.migration.fixups_complete' is incremented in this patch?

Then just drop this patch?

Matt

>  			i--;
>  			continue;
> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf.c b/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
> index ff9fb9196486..240c53b07eb3 100644
> --- a/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
> @@ -1254,6 +1254,11 @@ static size_t post_migration_scratch_size(struct xe_device *xe)
>  	return max(xe_lrc_reg_size(xe), LRC_WA_BB_SIZE);
>  }
>  
> +int xe_vf_migration_fixups_complete_count(struct xe_gt *gt)
> +{
> +	return atomic_read(&gt->sriov.vf.migration.fixups_complete);
> +}
> +
>  static int vf_post_migration_fixups(struct xe_gt *gt)
>  {
>  	void *buf = gt->sriov.vf.migration.scratch;
> @@ -1274,6 +1279,8 @@ static int vf_post_migration_fixups(struct xe_gt *gt)
>  	if (err)
>  		return err;
>  
> +	atomic_inc(&gt->sriov.vf.migration.fixups_complete);
> +
>  	return 0;
>  }
>  
> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf.h b/drivers/gpu/drm/xe/xe_gt_sriov_vf.h
> index 8c21b8ab2f16..4651c7f3335c 100644
> --- a/drivers/gpu/drm/xe/xe_gt_sriov_vf.h
> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_vf.h
> @@ -41,5 +41,6 @@ void xe_gt_sriov_vf_print_version(struct xe_gt *gt, struct drm_printer *p);
>  
>  bool xe_gt_vf_valid_default_lrc(struct xe_gt *gt);
>  void xe_gt_sriov_vf_wait_valid_default_lrc(struct xe_gt *gt);
> +int xe_vf_migration_fixups_complete_count(struct xe_gt *gt);
>  
>  #endif
> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h b/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h
> index 8be181bf3cf3..41d6199e3508 100644
> --- a/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h
> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h
> @@ -54,6 +54,8 @@ struct xe_gt_sriov_vf_migration {
>  	wait_queue_head_t wq;
>  	/** @scratch: Scratch memory for VF recovery */
>  	void *scratch;
> +	/** @fixups_complete: Counts completed fixups stages */
> +	atomic_t fixups_complete;
>  	/** @debug: Debug hooks for delaying migration */
>  	struct {
>  		/**
> -- 
> 2.25.1
>