[Intel-xe] [PATCH v5 02/10] drm/xe/tlb: ensure we access seqno_recv once

[Matthew Brost]

On Thu, Jul 06, 2023 at 05:20:06PM +0100, Matthew Auld wrote:
> Ensure we load gt->tlb_invalidation.seqno_recv once, and use that for
> our seqno checking. The gt->tlb_invalidation_seqno_past is a shared
> global variable and can potentially change at any point here.  However
> the checks here need to operate on a stable version of seqno_recv for
> this to make any sense.
> 
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Matthew Brost <matthew.brost at intel.com>

Reviewed-by: Matthew Brost <matthew.brost at intel.com>

> Cc: José Roberto de Souza <jose.souza at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> index 08432f472e2d..c67abc67d9fc 100644
> --- a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> +++ b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> @@ -257,15 +257,15 @@ int xe_gt_tlb_invalidation_vma(struct xe_gt *gt,
>  
>  static bool tlb_invalidation_seqno_past(struct xe_gt *gt, int seqno)
>  {
> -	if (seqno - gt->tlb_invalidation.seqno_recv <
> -	    -(TLB_INVALIDATION_SEQNO_MAX / 2))
> +	int seqno_recv = READ_ONCE(gt->tlb_invalidation.seqno_recv);
> +
> +	if (seqno - seqno_recv < -(TLB_INVALIDATION_SEQNO_MAX / 2))
>  		return false;
>  
> -	if (seqno - gt->tlb_invalidation.seqno_recv >
> -	    (TLB_INVALIDATION_SEQNO_MAX / 2))
> +	if (seqno - seqno_recv > (TLB_INVALIDATION_SEQNO_MAX / 2))
>  		return true;
>  
> -	return gt->tlb_invalidation.seqno_recv >= seqno;
> +	return seqno_recv >= seqno;
>  }
>  
>  /**
> @@ -337,7 +337,7 @@ int xe_guc_tlb_invalidation_done_handler(struct xe_guc *guc, u32 *msg, u32 len)
>  	 * wake_up_all() and wait_event_timeout() already have the correct
>  	 * barriers.
>  	 */
> -	gt->tlb_invalidation.seqno_recv = msg[0];
> +	WRITE_ONCE(gt->tlb_invalidation.seqno_recv, msg[0]);
>  	wake_up_all(&guc->ct.wq);
>  
>  	fence = list_first_entry_or_null(&gt->tlb_invalidation.pending_fences,
> -- 
> 2.41.0
>