[Intel-xe] [PATCH] drm/xe: Fix potential deadlock handling page faults

[Matthew Brost]

Within a class the GuC will hault scheduling if the head of the queue
can't be scheduled the queue will block. This can lead to deadlock if
BCS0-7 all have faults and another engine on BCS0-7 is at head of the
GuC scheduling queue as the migration engine used to fix tthe fault will
be blocked. To work around this set the migration engine to the highest
priority when servicing page faults.

Signed-off-by: Matthew Brost <matthew.brost at intel.com>
---
 drivers/gpu/drm/xe/xe_gt_pagefault.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_gt_pagefault.c b/drivers/gpu/drm/xe/xe_gt_pagefault.c
index 76ec40567a78..8fad6e60f826 100644
--- a/drivers/gpu/drm/xe/xe_gt_pagefault.c
+++ b/drivers/gpu/drm/xe/xe_gt_pagefault.c
@@ -106,6 +106,7 @@ static struct xe_vma *lookup_vma(struct xe_vm *vm, u64 page_addr)
 static int handle_pagefault(struct xe_gt *gt, struct pagefault *pf)
 {
 	struct xe_device *xe = gt_to_xe(gt);
+	struct xe_engine *e = xe_gt_migrate_engine(gt);
 	struct xe_vm *vm;
 	struct xe_vma *vma = NULL;
 	struct xe_bo *bo;
@@ -185,6 +186,7 @@ static int handle_pagefault(struct xe_gt *gt, struct pagefault *pf)
 	if (ret)
 		goto unlock_vm;
 
+	e->ops->set_priority(e, DRM_SCHED_PRIORITY_KERNEL);
 	if (atomic) {
 		if (xe_vma_is_userptr(vma)) {
 			ret = -EACCES;
@@ -204,7 +206,7 @@ static int handle_pagefault(struct xe_gt *gt, struct pagefault *pf)
 
 	/* Bind VMA only to the GT that has faulted */
 	trace_xe_vma_pf_bind(vma);
-	fence = __xe_pt_bind_vma(gt, vma, xe_gt_migrate_engine(gt), NULL, 0,
+	fence = __xe_pt_bind_vma(gt, vma, e, NULL, 0,
 				 vma->gt_present & BIT(gt->info.id));
 	if (IS_ERR(fence)) {
 		ret = PTR_ERR(fence);
@@ -218,6 +220,7 @@ static int handle_pagefault(struct xe_gt *gt, struct pagefault *pf)
 	 */
 	dma_fence_wait(fence, false);
 	dma_fence_put(fence);
+	e->ops->set_priority(e, DRM_SCHED_PRIORITY_NORMAL);
 
 	if (xe_vma_is_userptr(vma))
 		ret = xe_vma_userptr_check_repin(vma);
-- 
2.34.1