drm/xe/pt: check no-DMA huge-pte cases before DMA segment test

On a non-range clear, curs.size is never set, so the segment test
(next - va_curs_start > curs->size) returns false for every level > 0
before the clear_pt short-circuit is reached. The clear then descends to
level 0 instead of forming a huge zero-leaf, wasting page tables and
risking -ENOMEM on unbind.

Move the null-VMA, purged-BO and clear_pt short-circuits above the
curs->size test. The bind path always sets curs.size, so it is unaffected.

v2
- Also set curs.size on the clear path so the cursor stays meaningful
during the walk. clear_pt is only reached with range == NULL, so assert
that invariant. (Matthew Brost)

Cc: Matthew Brost <matthew.brost@intel.com>
Fixes: 5b658b7e89c3 ("drm/xe: Clear scratch page on vm_bind")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260728055916.593707-2-himal.prasad.ghimiray@intel.com
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
index 598c6b2571e7..0e9d669620b9 100644
--- a/drivers/gpu/drm/xe/xe_pt.c
+++ b/drivers/gpu/drm/xe/xe_pt.c
@@ -443,10 +443,6 @@ static bool xe_pt_hugepte_possible(u64 addr, u64 next, unsigned int level,
 	if (!xe_pt_covers(addr, next, level, &xe_walk->base))
 		return false;
 
-	/* Does the DMA segment cover the whole pte? */
-	if (next - xe_walk->va_curs_start > xe_walk->curs->size)
-		return false;
-
 	/* null VMA's and purged BO's do not have dma addresses */
 	if (xe_vma_is_null(xe_walk->vma) || (bo && xe_bo_is_purged(bo)))
 		return true;
@@ -455,6 +451,10 @@ static bool xe_pt_hugepte_possible(u64 addr, u64 next, unsigned int level,
 	if (xe_walk->clear_pt)
 		return true;
 
+	/* Does the DMA segment cover the whole pte? */
+	if (next - xe_walk->va_curs_start > xe_walk->curs->size)
+		return false;
+
 	/* Is the DMA address huge PTE size aligned? */
 	size = next - addr;
 	dma = addr - xe_walk->va_curs_start + xe_res_dma(xe_walk->curs);
@@ -775,8 +775,11 @@ xe_pt_stage_bind(struct xe_tile *tile, struct xe_vma *vma,
 	}
 
 	xe_walk.needs_64K = (vm->flags & XE_VM_FLAG_64K);
-	if (clear_pt)
+	if (clear_pt) {
+		xe_assert(xe, !range);
+		curs.size = xe_vma_size(vma);
 		goto walk_pt;
+	}
 
 	if (vma->gpuva.flags & XE_VMA_ATOMIC_PTE_BIT) {
 		xe_walk.default_vram_pte = xe_atomic_for_vram(vm, vma) ? XE_USM_PPGTT_PTE_AE : 0;