[PATCH v2 0/3] Userptr fixes

[PATCH v2 0/3] Userptr fixes

[Matthew Brost]

Tested with below tests on BMG + CONFIG_DRM_XE_USERPTR_INVAL_INJECT
xe_exec_basic; xe_exec_compute_mode; xe_exec_fault_mode; xe_vm; xe_exec_threads

Including a patch from Matt Auld as it required for above test case to pass.

Matt

Matthew Auld (1):
  drm/xe/userptr: fix EFAULT handling

Matthew Brost (2):
  drm/xe: Userptr invalidation race with binds fixes
  drm/xe: Add staging tree for VM binds

 drivers/gpu/drm/xe/xe_pt.c       | 194 +++++++++++++++++++++++--------
 drivers/gpu/drm/xe/xe_pt_types.h |   3 +-
 drivers/gpu/drm/xe/xe_pt_walk.c  |   3 +-
 drivers/gpu/drm/xe/xe_pt_walk.h  |   4 +
 drivers/gpu/drm/xe/xe_vm.c       |  16 ++-
 5 files changed, 170 insertions(+), 50 deletions(-)

-- 
2.34.1

[PATCH v2 1/3] drm/xe/userptr: fix EFAULT handling

[Matthew Brost]

From: Matthew Auld <matthew.auld@intel.com>

Currently we treat EFAULT from hmm_range_fault() as a non-fatal error
when called from xe_vm_userptr_pin() with the idea that we want to avoid
killing the entire vm and chucking an error, under the assumption that
the user just did an unmap or something, and has no intention of
actually touching that memory from the GPU.  At this point we have
already zapped the PTEs so any access should generate a page fault, and
if the pin fails there also it will then become fatal.

However it looks like it's possible for the userptr vma to still be on
the rebind list in preempt_rebind_work_func(), if we had to retry the
pin again due to something happening in the caller before we did the
rebind step, but in the meantime needing to re-validate the userptr and
this time hitting the EFAULT.

This might explain an internal user report of hitting:

[  191.738349] WARNING: CPU: 1 PID: 157 at drivers/gpu/drm/xe/xe_res_cursor.h:158 xe_pt_stage_bind.constprop.0+0x60a/0x6b0 [xe]
[  191.738551] Workqueue: xe-ordered-wq preempt_rebind_work_func [xe]
[  191.738616] RIP: 0010:xe_pt_stage_bind.constprop.0+0x60a/0x6b0 [xe]
[  191.738690] Call Trace:
[  191.738692]  <TASK>
[  191.738694]  ? show_regs+0x69/0x80
[  191.738698]  ? __warn+0x93/0x1a0
[  191.738703]  ? xe_pt_stage_bind.constprop.0+0x60a/0x6b0 [xe]
[  191.738759]  ? report_bug+0x18f/0x1a0
[  191.738764]  ? handle_bug+0x63/0xa0
[  191.738767]  ? exc_invalid_op+0x19/0x70
[  191.738770]  ? asm_exc_invalid_op+0x1b/0x20
[  191.738777]  ? xe_pt_stage_bind.constprop.0+0x60a/0x6b0 [xe]
[  191.738834]  ? ret_from_fork_asm+0x1a/0x30
[  191.738849]  bind_op_prepare+0x105/0x7b0 [xe]
[  191.738906]  ? dma_resv_reserve_fences+0x301/0x380
[  191.738912]  xe_pt_update_ops_prepare+0x28c/0x4b0 [xe]
[  191.738966]  ? kmemleak_alloc+0x4b/0x80
[  191.738973]  ops_execute+0x188/0x9d0 [xe]
[  191.739036]  xe_vm_rebind+0x4ce/0x5a0 [xe]
[  191.739098]  ? trace_hardirqs_on+0x4d/0x60
[  191.739112]  preempt_rebind_work_func+0x76f/0xd00 [xe]

Followed by NPD, when running some workload, since the sg was never
actually populated but the vma is still marked for rebind when it should
be skipped for this special EFAULT case. And from the logs it does seem
like we hit this special EFAULT case before the explosions.

v2 (MattB):
 - Move earlier

Fixes: 521db22a1d70 ("drm/xe: Invalidate userptr VMA on page pin fault")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: <stable@vger.kernel.org> # v6.10+
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 drivers/gpu/drm/xe/xe_vm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index d664f2e418b2..ea2e287e6526 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -681,6 +681,18 @@ int xe_vm_userptr_pin(struct xe_vm *vm)
 		err = xe_vma_userptr_pin_pages(uvma);
 		if (err == -EFAULT) {
 			list_del_init(&uvma->userptr.repin_link);
+			/*
+			 * We might have already done the pin once already, but
+			 * then had to retry before the re-bind happened, due
+			 * some other condition in the caller, but in the
+			 * meantime the userptr got dinged by the notifier such
+			 * that we need to revalidate here, but this time we hit
+			 * the EFAULT. In such a case make sure we remove
+			 * ourselves from the rebind list to avoid going down in
+			 * flames.
+			 */
+			if (!list_empty(&uvma->vma.combined_links.rebind))
+				list_del_init(&uvma->vma.combined_links.rebind);
 
 			/* Wait for pending binds */
 			xe_vm_lock(vm, false);
-- 
2.34.1

[PATCH v2 2/3] drm/xe: Userptr invalidation race with binds fixes

[Matthew Brost]

Squash bind operation after userptr invalidation into a clearing of
PTEs. Will prevent valid GPU page tables from pointing to stale CPU
pages.

Fixup initial bind handling always add VMAs to invalidation list and
clear PTEs.

Remove unused rebind variable in xe_pt.

Always hold notifier across TLB invalidation in notifier to prevent a
UAF if an unbind races.

Including all of the above changes for Fixes patch in hopes of an easier
backport which fix a single patch.

v2:
 - Wait dma-resv bookkeep before issuing PTE zap (Thomas)
 - Support scratch page on invalidation (Thomas)

Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: <stable@vger.kernel.org>
Fixes: e8babb280b5e ("drm/xe: Convert multiple bind ops into single job")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/xe/xe_pt.c       | 146 +++++++++++++++++++++++--------
 drivers/gpu/drm/xe/xe_pt_types.h |   3 +-
 drivers/gpu/drm/xe/xe_vm.c       |   4 +-
 3 files changed, 115 insertions(+), 38 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
index 1ddcc7e79a93..add521b5c6ae 100644
--- a/drivers/gpu/drm/xe/xe_pt.c
+++ b/drivers/gpu/drm/xe/xe_pt.c
@@ -351,7 +351,8 @@ xe_pt_new_shared(struct xe_walk_update *wupd, struct xe_pt *parent,
  */
 static int
 xe_pt_insert_entry(struct xe_pt_stage_bind_walk *xe_walk, struct xe_pt *parent,
-		   pgoff_t offset, struct xe_pt *xe_child, u64 pte)
+		   pgoff_t offset, struct xe_pt *xe_child, u64 pte,
+		   unsigned int level)
 {
 	struct xe_pt_update *upd = &xe_walk->wupd.updates[parent->level];
 	struct xe_pt_update *child_upd = xe_child ?
@@ -389,6 +390,9 @@ xe_pt_insert_entry(struct xe_pt_stage_bind_walk *xe_walk, struct xe_pt *parent,
 		idx = offset - entry->ofs;
 		entry->pt_entries[idx].pt = xe_child;
 		entry->pt_entries[idx].pte = pte;
+		entry->pt_entries[idx].level = level;
+		if (likely(!xe_child))
+			entry->pt_entries[idx].level |= XE_PT_IS_LEAF;
 		entry->qwords++;
 	}
 
@@ -515,7 +519,8 @@ xe_pt_stage_bind_entry(struct xe_ptw *parent, pgoff_t offset,
 			}
 		}
 
-		ret = xe_pt_insert_entry(xe_walk, xe_parent, offset, NULL, pte);
+		ret = xe_pt_insert_entry(xe_walk, xe_parent, offset, NULL, pte,
+					 level);
 		if (unlikely(ret))
 			return ret;
 
@@ -571,7 +576,7 @@ xe_pt_stage_bind_entry(struct xe_ptw *parent, pgoff_t offset,
 
 		pte = vm->pt_ops->pde_encode_bo(xe_child->bo, 0, pat_index) | flags;
 		ret = xe_pt_insert_entry(xe_walk, xe_parent, offset, xe_child,
-					 pte);
+					 pte, level);
 	}
 
 	*action = ACTION_SUBTREE;
@@ -752,6 +757,10 @@ struct xe_pt_zap_ptes_walk {
 	/* Input parameters for the walk */
 	/** @tile: The tile we're building for */
 	struct xe_tile *tile;
+	/** @vm: VM we're building for */
+	struct xe_vm *vm;
+	/** @scratch: write entries with scratch */
+	bool scratch;
 
 	/* Output */
 	/** @needs_invalidate: Whether we need to invalidate TLB*/
@@ -779,9 +788,18 @@ static int xe_pt_zap_ptes_entry(struct xe_ptw *parent, pgoff_t offset,
 	 */
 	if (xe_pt_nonshared_offsets(addr, next, --level, walk, action, &offset,
 				    &end_offset)) {
-		xe_map_memset(tile_to_xe(xe_walk->tile), &xe_child->bo->vmap,
-			      offset * sizeof(u64), 0,
-			      (end_offset - offset) * sizeof(u64));
+		if (unlikely(xe_walk->scratch)) {
+			u64 pte = __xe_pt_empty_pte(xe_walk->tile, xe_walk->vm,
+						    level);
+
+			for (; offset < end_offset; ++offset)
+				xe_pt_write(tile_to_xe(xe_walk->tile),
+					    &xe_child->bo->vmap, offset, pte);
+		} else {
+			xe_map_memset(tile_to_xe(xe_walk->tile), &xe_child->bo->vmap,
+				      offset * sizeof(u64), 0,
+				      (end_offset - offset) * sizeof(u64));
+		}
 		xe_walk->needs_invalidate = true;
 	}
 
@@ -792,6 +810,31 @@ static const struct xe_pt_walk_ops xe_pt_zap_ptes_ops = {
 	.pt_entry = xe_pt_zap_ptes_entry,
 };
 
+struct xe_pt_zap_ptes_flags {
+	bool scratch:1;
+};
+
+static bool __xe_pt_zap_ptes(struct xe_tile *tile, struct xe_vma *vma,
+			     struct xe_pt_zap_ptes_flags flags)
+{
+	struct xe_pt_zap_ptes_walk xe_walk = {
+		.base = {
+			.ops = &xe_pt_zap_ptes_ops,
+			.shifts = xe_normal_pt_shifts,
+			.max_level = XE_PT_HIGHEST_LEVEL,
+		},
+		.tile = tile,
+		.vm = xe_vma_vm(vma),
+		.scratch = flags.scratch,
+	};
+	struct xe_pt *pt = xe_vma_vm(vma)->pt_root[tile->id];
+
+	(void)xe_pt_walk_shared(&pt->base, pt->level, xe_vma_start(vma),
+				xe_vma_end(vma), &xe_walk.base);
+
+	return xe_walk.needs_invalidate;
+}
+
 /**
  * xe_pt_zap_ptes() - Zap (zero) gpu ptes of an address range
  * @tile: The tile we're zapping for.
@@ -810,24 +853,13 @@ static const struct xe_pt_walk_ops xe_pt_zap_ptes_ops = {
  */
 bool xe_pt_zap_ptes(struct xe_tile *tile, struct xe_vma *vma)
 {
-	struct xe_pt_zap_ptes_walk xe_walk = {
-		.base = {
-			.ops = &xe_pt_zap_ptes_ops,
-			.shifts = xe_normal_pt_shifts,
-			.max_level = XE_PT_HIGHEST_LEVEL,
-		},
-		.tile = tile,
-	};
-	struct xe_pt *pt = xe_vma_vm(vma)->pt_root[tile->id];
+	struct xe_pt_zap_ptes_flags flags = {};
 	u8 pt_mask = (vma->tile_present & ~vma->tile_invalidated);
 
 	if (!(pt_mask & BIT(tile->id)))
 		return false;
 
-	(void)xe_pt_walk_shared(&pt->base, pt->level, xe_vma_start(vma),
-				xe_vma_end(vma), &xe_walk.base);
-
-	return xe_walk.needs_invalidate;
+	return __xe_pt_zap_ptes(tile, vma, flags);
 }
 
 static void
@@ -1201,7 +1233,46 @@ static bool xe_pt_userptr_inject_eagain(struct xe_userptr_vma *uvma)
 
 #endif
 
-static int vma_check_userptr(struct xe_vm *vm, struct xe_vma *vma,
+static void
+vma_convert_to_invalidation(struct xe_tile *tile, struct xe_vma *vma,
+			    struct xe_vm_pgtable_update_ops *pt_update)
+{
+	struct xe_pt_zap_ptes_flags flags = { .scratch = true, };
+	int i, j, k;
+
+	/*
+	 * Need to update this function to bypass scratch setup if in fault mode
+	 */
+	xe_assert(xe_vma_vm(vma)->xe, !xe_vm_in_fault_mode(xe_vma_vm(vma)));
+
+	for (i = 0; i < pt_update->current_op; ++i) {
+		struct xe_vm_pgtable_update_op *op = &pt_update->ops[i];
+
+		if (vma != op->vma || (!op->bind && !op->rebind))
+			continue;
+
+		for (j = 0; j < op->num_entries; ++j) {
+			for (k = 0; k < op->entries[j].qwords; ++k) {
+				struct xe_pt_entry *entry =
+					&op->entries[j].pt_entries[k];
+				unsigned int level = entry->level;
+
+				if (!(level & XE_PT_IS_LEAF))
+					continue;
+
+				level &= ~XE_PT_IS_LEAF;
+				entry->pte = __xe_pt_empty_pte(tile,
+							       xe_vma_vm(vma),
+							       level);
+			}
+		}
+	}
+
+	__xe_pt_zap_ptes(tile, vma, flags);
+}
+
+static int vma_check_userptr(struct xe_tile *tile, struct xe_vm *vm,
+			     struct xe_vma *vma,
 			     struct xe_vm_pgtable_update_ops *pt_update)
 {
 	struct xe_userptr_vma *uvma;
@@ -1215,9 +1286,6 @@ static int vma_check_userptr(struct xe_vm *vm, struct xe_vma *vma,
 	uvma = to_userptr_vma(vma);
 	notifier_seq = uvma->userptr.notifier_seq;
 
-	if (uvma->userptr.initial_bind && !xe_vm_in_fault_mode(vm))
-		return 0;
-
 	if (!mmu_interval_read_retry(&uvma->userptr.notifier,
 				     notifier_seq) &&
 	    !xe_pt_userptr_inject_eagain(uvma))
@@ -1226,6 +1294,8 @@ static int vma_check_userptr(struct xe_vm *vm, struct xe_vma *vma,
 	if (xe_vm_in_fault_mode(vm)) {
 		return -EAGAIN;
 	} else {
+		long err;
+
 		spin_lock(&vm->userptr.invalidated_lock);
 		list_move_tail(&uvma->userptr.invalidate_link,
 			       &vm->userptr.invalidated);
@@ -1234,25 +1304,27 @@ static int vma_check_userptr(struct xe_vm *vm, struct xe_vma *vma,
 		if (xe_vm_in_preempt_fence_mode(vm)) {
 			struct dma_resv_iter cursor;
 			struct dma_fence *fence;
-			long err;
 
 			dma_resv_iter_begin(&cursor, xe_vm_resv(vm),
 					    DMA_RESV_USAGE_BOOKKEEP);
 			dma_resv_for_each_fence_unlocked(&cursor, fence)
 				dma_fence_enable_sw_signaling(fence);
 			dma_resv_iter_end(&cursor);
-
-			err = dma_resv_wait_timeout(xe_vm_resv(vm),
-						    DMA_RESV_USAGE_BOOKKEEP,
-						    false, MAX_SCHEDULE_TIMEOUT);
-			XE_WARN_ON(err <= 0);
 		}
+
+		err = dma_resv_wait_timeout(xe_vm_resv(vm),
+					    DMA_RESV_USAGE_BOOKKEEP,
+					    false, MAX_SCHEDULE_TIMEOUT);
+		XE_WARN_ON(err <= 0);
+
+		vma_convert_to_invalidation(tile, vma, pt_update);
 	}
 
 	return 0;
 }
 
-static int op_check_userptr(struct xe_vm *vm, struct xe_vma_op *op,
+static int op_check_userptr(struct xe_tile *tile, struct xe_vm *vm,
+			    struct xe_vma_op *op,
 			    struct xe_vm_pgtable_update_ops *pt_update)
 {
 	int err = 0;
@@ -1264,18 +1336,21 @@ static int op_check_userptr(struct xe_vm *vm, struct xe_vma_op *op,
 		if (!op->map.immediate && xe_vm_in_fault_mode(vm))
 			break;
 
-		err = vma_check_userptr(vm, op->map.vma, pt_update);
+		err = vma_check_userptr(tile, vm, op->map.vma, pt_update);
 		break;
 	case DRM_GPUVA_OP_REMAP:
 		if (op->remap.prev)
-			err = vma_check_userptr(vm, op->remap.prev, pt_update);
+			err = vma_check_userptr(tile, vm, op->remap.prev,
+						pt_update);
 		if (!err && op->remap.next)
-			err = vma_check_userptr(vm, op->remap.next, pt_update);
+			err = vma_check_userptr(tile, vm, op->remap.next,
+						pt_update);
 		break;
 	case DRM_GPUVA_OP_UNMAP:
 		break;
 	case DRM_GPUVA_OP_PREFETCH:
-		err = vma_check_userptr(vm, gpuva_to_vma(op->base.prefetch.va),
+		err = vma_check_userptr(tile, vm,
+					gpuva_to_vma(op->base.prefetch.va),
 					pt_update);
 		break;
 	default:
@@ -1301,7 +1376,8 @@ static int xe_pt_userptr_pre_commit(struct xe_migrate_pt_update *pt_update)
 	down_read(&vm->userptr.notifier_lock);
 
 	list_for_each_entry(op, &vops->list, link) {
-		err = op_check_userptr(vm, op, pt_update_ops);
+		err = op_check_userptr(&vm->xe->tiles[pt_update->tile_id],
+				       vm, op, pt_update_ops);
 		if (err) {
 			up_read(&vm->userptr.notifier_lock);
 			break;
diff --git a/drivers/gpu/drm/xe/xe_pt_types.h b/drivers/gpu/drm/xe/xe_pt_types.h
index 384cc04de719..6f99ff2b8fce 100644
--- a/drivers/gpu/drm/xe/xe_pt_types.h
+++ b/drivers/gpu/drm/xe/xe_pt_types.h
@@ -29,7 +29,6 @@ struct xe_pt {
 	struct xe_bo *bo;
 	unsigned int level;
 	unsigned int num_live;
-	bool rebind;
 	bool is_compact;
 #if IS_ENABLED(CONFIG_DRM_XE_DEBUG_VM)
 	/** addr: Virtual address start address of the PT. */
@@ -52,6 +51,8 @@ struct xe_pt_ops {
 struct xe_pt_entry {
 	struct xe_pt *pt;
 	u64 pte;
+#define XE_PT_IS_LEAF	BIT(31)
+	unsigned int level;
 };
 
 struct xe_vm_pgtable_update {
diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index ea2e287e6526..f90e5c92010c 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -623,8 +623,6 @@ static bool vma_userptr_invalidate(struct mmu_interval_notifier *mni,
 		spin_unlock(&vm->userptr.invalidated_lock);
 	}
 
-	up_write(&vm->userptr.notifier_lock);
-
 	/*
 	 * Preempt fences turn into schedule disables, pipeline these.
 	 * Note that even in fault mode, we need to wait for binds and
@@ -647,6 +645,8 @@ static bool vma_userptr_invalidate(struct mmu_interval_notifier *mni,
 		XE_WARN_ON(err);
 	}
 
+	up_write(&vm->userptr.notifier_lock);
+
 	trace_xe_vma_userptr_invalidate_complete(vma);
 
 	return true;
-- 
2.34.1

[PATCH v2 3/3] drm/xe: Add staging tree for VM binds

[Matthew Brost]

Concurrent VM bind staging and zapping of PTEs from a userptr notifier
do not work because the view of PTEs is not stable. VM binds cannot
acquire the notifier lock during staging, as memory allocations are
required. To resolve this race condition, use a staging tree for VM
binds that is committed only under the userptr notifier lock during the
final step of the bind. This ensures a consistent view of the PTEs in
the userptr notifier.

A follow up may only use staging for VM in fault mode as this is the
only mode in which the above race exists.

Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: <stable@vger.kernel.org>
Fixes: e8babb280b5e ("drm/xe: Convert multiple bind ops into single job")
Fixes: a708f6501c69 ("drm/xe: Update PT layer with better error handling")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/xe/xe_pt.c      | 50 +++++++++++++++++++++++++--------
 drivers/gpu/drm/xe/xe_pt_walk.c |  3 +-
 drivers/gpu/drm/xe/xe_pt_walk.h |  4 +++
 3 files changed, 44 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
index add521b5c6ae..118b81cd7205 100644
--- a/drivers/gpu/drm/xe/xe_pt.c
+++ b/drivers/gpu/drm/xe/xe_pt.c
@@ -28,6 +28,8 @@ struct xe_pt_dir {
 	struct xe_pt pt;
 	/** @children: Array of page-table child nodes */
 	struct xe_ptw *children[XE_PDES];
+	/** @staging: Array of page-table staging nodes */
+	struct xe_ptw *staging[XE_PDES];
 };
 
 #if IS_ENABLED(CONFIG_DRM_XE_DEBUG_VM)
@@ -50,7 +52,7 @@ static struct xe_pt_dir *as_xe_pt_dir(struct xe_pt *pt)
 
 static struct xe_pt *xe_pt_entry(struct xe_pt_dir *pt_dir, unsigned int index)
 {
-	return container_of(pt_dir->children[index], struct xe_pt, base);
+	return container_of(pt_dir->staging[index], struct xe_pt, base);
 }
 
 static u64 __xe_pt_empty_pte(struct xe_tile *tile, struct xe_vm *vm,
@@ -125,6 +127,7 @@ struct xe_pt *xe_pt_create(struct xe_vm *vm, struct xe_tile *tile,
 	}
 	pt->bo = bo;
 	pt->base.children = level ? as_xe_pt_dir(pt)->children : NULL;
+	pt->base.staging = level ? as_xe_pt_dir(pt)->staging : NULL;
 
 	if (vm->xef)
 		xe_drm_client_add_bo(vm->xef->client, pt->bo);
@@ -377,8 +380,10 @@ xe_pt_insert_entry(struct xe_pt_stage_bind_walk *xe_walk, struct xe_pt *parent,
 		/* Continue building a non-connected subtree. */
 		struct iosys_map *map = &parent->bo->vmap;
 
-		if (unlikely(xe_child))
+		if (unlikely(xe_child)) {
 			parent->base.children[offset] = &xe_child->base;
+			parent->base.staging[offset] = &xe_child->base;
+		}
 
 		xe_pt_write(xe_walk->vm->xe, map, offset, pte);
 		parent->num_live++;
@@ -619,6 +624,7 @@ xe_pt_stage_bind(struct xe_tile *tile, struct xe_vma *vma,
 			.ops = &xe_pt_stage_bind_ops,
 			.shifts = xe_normal_pt_shifts,
 			.max_level = XE_PT_HIGHEST_LEVEL,
+			.staging = true,
 		},
 		.vm = xe_vma_vm(vma),
 		.tile = tile,
@@ -812,6 +818,7 @@ static const struct xe_pt_walk_ops xe_pt_zap_ptes_ops = {
 
 struct xe_pt_zap_ptes_flags {
 	bool scratch:1;
+	bool staging:1;
 };
 
 static bool __xe_pt_zap_ptes(struct xe_tile *tile, struct xe_vma *vma,
@@ -822,6 +829,7 @@ static bool __xe_pt_zap_ptes(struct xe_tile *tile, struct xe_vma *vma,
 			.ops = &xe_pt_zap_ptes_ops,
 			.shifts = xe_normal_pt_shifts,
 			.max_level = XE_PT_HIGHEST_LEVEL,
+			.staging = flags.staging,
 		},
 		.tile = tile,
 		.vm = xe_vma_vm(vma),
@@ -905,7 +913,7 @@ static void xe_pt_cancel_bind(struct xe_vma *vma,
 	}
 }
 
-static void xe_pt_commit_locks_assert(struct xe_vma *vma)
+static void xe_pt_commit_prepare_locks_assert(struct xe_vma *vma)
 {
 	struct xe_vm *vm = xe_vma_vm(vma);
 
@@ -917,6 +925,16 @@ static void xe_pt_commit_locks_assert(struct xe_vma *vma)
 	xe_vm_assert_held(vm);
 }
 
+static void xe_pt_commit_locks_assert(struct xe_vma *vma)
+{
+	struct xe_vm *vm = xe_vma_vm(vma);
+
+	xe_pt_commit_prepare_locks_assert(vma);
+
+	if (xe_vma_is_userptr(vma))
+		lockdep_assert_held_read(&vm->userptr.notifier_lock);
+}
+
 static void xe_pt_commit(struct xe_vma *vma,
 			 struct xe_vm_pgtable_update *entries,
 			 u32 num_entries, struct llist_head *deferred)
@@ -927,13 +945,17 @@ static void xe_pt_commit(struct xe_vma *vma,
 
 	for (i = 0; i < num_entries; i++) {
 		struct xe_pt *pt = entries[i].pt;
+		struct xe_pt_dir *pt_dir;
 
 		if (!pt->level)
 			continue;
 
+		pt_dir = as_xe_pt_dir(pt);
 		for (j = 0; j < entries[i].qwords; j++) {
 			struct xe_pt *oldpte = entries[i].pt_entries[j].pt;
+			int j_ = j + entries[i].ofs;
 
+			pt_dir->children[j_] = pt_dir->staging[j_];
 			xe_pt_destroy(oldpte, xe_vma_vm(vma)->flags, deferred);
 		}
 	}
@@ -945,7 +967,7 @@ static void xe_pt_abort_bind(struct xe_vma *vma,
 {
 	int i, j;
 
-	xe_pt_commit_locks_assert(vma);
+	xe_pt_commit_prepare_locks_assert(vma);
 
 	for (i = num_entries - 1; i >= 0; --i) {
 		struct xe_pt *pt = entries[i].pt;
@@ -963,7 +985,7 @@ static void xe_pt_abort_bind(struct xe_vma *vma,
 			struct xe_pt *newpte = xe_pt_entry(pt_dir, j_);
 			struct xe_pt *oldpte = entries[i].pt_entries[j].pt;
 
-			pt_dir->children[j_] = oldpte ? &oldpte->base : 0;
+			pt_dir->staging[j_] = oldpte ? &oldpte->base : 0;
 			xe_pt_destroy(newpte, xe_vma_vm(vma)->flags, NULL);
 		}
 	}
@@ -975,7 +997,7 @@ static void xe_pt_commit_prepare_bind(struct xe_vma *vma,
 {
 	u32 i, j;
 
-	xe_pt_commit_locks_assert(vma);
+	xe_pt_commit_prepare_locks_assert(vma);
 
 	for (i = 0; i < num_entries; i++) {
 		struct xe_pt *pt = entries[i].pt;
@@ -996,7 +1018,7 @@ static void xe_pt_commit_prepare_bind(struct xe_vma *vma,
 			if (xe_pt_entry(pt_dir, j_))
 				oldpte = xe_pt_entry(pt_dir, j_);
 
-			pt_dir->children[j_] = &newpte->base;
+			pt_dir->staging[j_] = &newpte->base;
 			entries[i].pt_entries[j].pt = oldpte;
 		}
 	}
@@ -1237,7 +1259,10 @@ static void
 vma_convert_to_invalidation(struct xe_tile *tile, struct xe_vma *vma,
 			    struct xe_vm_pgtable_update_ops *pt_update)
 {
-	struct xe_pt_zap_ptes_flags flags = { .scratch = true, };
+	struct xe_pt_zap_ptes_flags flags = {
+		.scratch = true,
+		.staging = true,
+	};
 	int i, j, k;
 
 	/*
@@ -1590,6 +1615,7 @@ static unsigned int xe_pt_stage_unbind(struct xe_tile *tile, struct xe_vma *vma,
 			.ops = &xe_pt_stage_unbind_ops,
 			.shifts = xe_normal_pt_shifts,
 			.max_level = XE_PT_HIGHEST_LEVEL,
+			.staging = true,
 		},
 		.tile = tile,
 		.modified_start = xe_vma_start(vma),
@@ -1631,7 +1657,7 @@ static void xe_pt_abort_unbind(struct xe_vma *vma,
 {
 	int i, j;
 
-	xe_pt_commit_locks_assert(vma);
+	xe_pt_commit_prepare_locks_assert(vma);
 
 	for (i = num_entries - 1; i >= 0; --i) {
 		struct xe_vm_pgtable_update *entry = &entries[i];
@@ -1644,7 +1670,7 @@ static void xe_pt_abort_unbind(struct xe_vma *vma,
 			continue;
 
 		for (j = entry->ofs; j < entry->ofs + entry->qwords; j++)
-			pt_dir->children[j] =
+			pt_dir->staging[j] =
 				entries[i].pt_entries[j - entry->ofs].pt ?
 				&entries[i].pt_entries[j - entry->ofs].pt->base : NULL;
 	}
@@ -1657,7 +1683,7 @@ xe_pt_commit_prepare_unbind(struct xe_vma *vma,
 {
 	int i, j;
 
-	xe_pt_commit_locks_assert(vma);
+	xe_pt_commit_prepare_locks_assert(vma);
 
 	for (i = 0; i < num_entries; ++i) {
 		struct xe_vm_pgtable_update *entry = &entries[i];
@@ -1672,7 +1698,7 @@ xe_pt_commit_prepare_unbind(struct xe_vma *vma,
 		for (j = entry->ofs; j < entry->ofs + entry->qwords; j++) {
 			entry->pt_entries[j - entry->ofs].pt =
 				xe_pt_entry(pt_dir, j);
-			pt_dir->children[j] = NULL;
+			pt_dir->staging[j] = NULL;
 		}
 	}
 }
diff --git a/drivers/gpu/drm/xe/xe_pt_walk.c b/drivers/gpu/drm/xe/xe_pt_walk.c
index b8b3d2aea492..be602a763ff3 100644
--- a/drivers/gpu/drm/xe/xe_pt_walk.c
+++ b/drivers/gpu/drm/xe/xe_pt_walk.c
@@ -74,7 +74,8 @@ int xe_pt_walk_range(struct xe_ptw *parent, unsigned int level,
 		     u64 addr, u64 end, struct xe_pt_walk *walk)
 {
 	pgoff_t offset = xe_pt_offset(addr, level, walk);
-	struct xe_ptw **entries = parent->children ? parent->children : NULL;
+	struct xe_ptw **entries = walk->staging ? (parent->staging ?: NULL) :
+		(parent->children ?: NULL);
 	const struct xe_pt_walk_ops *ops = walk->ops;
 	enum page_walk_action action;
 	struct xe_ptw *child;
diff --git a/drivers/gpu/drm/xe/xe_pt_walk.h b/drivers/gpu/drm/xe/xe_pt_walk.h
index 5ecc4d2f0f65..5c02c244f7de 100644
--- a/drivers/gpu/drm/xe/xe_pt_walk.h
+++ b/drivers/gpu/drm/xe/xe_pt_walk.h
@@ -11,12 +11,14 @@
 /**
  * struct xe_ptw - base class for driver pagetable subclassing.
  * @children: Pointer to an array of children if any.
+ * @staging: Pointer to an array of staging if any.
  *
  * Drivers could subclass this, and if it's a page-directory, typically
  * embed an array of xe_ptw pointers.
  */
 struct xe_ptw {
 	struct xe_ptw **children;
+	struct xe_ptw **staging;
 };
 
 /**
@@ -41,6 +43,8 @@ struct xe_pt_walk {
 	 * as shared pagetables.
 	 */
 	bool shared_pt_mode;
+	/** @staging: Walk staging PT structure */
+	bool staging;
 };
 
 /**
-- 
2.34.1

[PATCH v2 3/3] drm/xe: Add staging tree for VM binds

[Matthew Brost]

Concurrent VM bind staging and zapping of PTEs from a userptr notifier
do not work because the view of PTEs is not stable. VM binds cannot
acquire the notifier lock during staging, as memory allocations are
required. To resolve this race condition, use a staging tree for VM
binds that is committed only under the userptr notifier lock during the
final step of the bind. This ensures a consistent view of the PTEs in
the userptr notifier.

A follow up may only use staging for VM in fault mode as this is the
only mode in which the above race exists.

Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: <stable@vger.kernel.org>
Fixes: e8babb280b5e ("drm/xe: Convert multiple bind ops into single job")
Fixes: a708f6501c69 ("drm/xe: Update PT layer with better error handling")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/xe/xe_pt.c      | 50 +++++++++++++++++++++++++--------
 drivers/gpu/drm/xe/xe_pt_walk.c |  3 +-
 drivers/gpu/drm/xe/xe_pt_walk.h |  4 +++
 3 files changed, 44 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
index add521b5c6ae..118b81cd7205 100644
--- a/drivers/gpu/drm/xe/xe_pt.c
+++ b/drivers/gpu/drm/xe/xe_pt.c
@@ -28,6 +28,8 @@ struct xe_pt_dir {
 	struct xe_pt pt;
 	/** @children: Array of page-table child nodes */
 	struct xe_ptw *children[XE_PDES];
+	/** @staging: Array of page-table staging nodes */
+	struct xe_ptw *staging[XE_PDES];
 };
 
 #if IS_ENABLED(CONFIG_DRM_XE_DEBUG_VM)
@@ -50,7 +52,7 @@ static struct xe_pt_dir *as_xe_pt_dir(struct xe_pt *pt)
 
 static struct xe_pt *xe_pt_entry(struct xe_pt_dir *pt_dir, unsigned int index)
 {
-	return container_of(pt_dir->children[index], struct xe_pt, base);
+	return container_of(pt_dir->staging[index], struct xe_pt, base);
 }
 
 static u64 __xe_pt_empty_pte(struct xe_tile *tile, struct xe_vm *vm,
@@ -125,6 +127,7 @@ struct xe_pt *xe_pt_create(struct xe_vm *vm, struct xe_tile *tile,
 	}
 	pt->bo = bo;
 	pt->base.children = level ? as_xe_pt_dir(pt)->children : NULL;
+	pt->base.staging = level ? as_xe_pt_dir(pt)->staging : NULL;
 
 	if (vm->xef)
 		xe_drm_client_add_bo(vm->xef->client, pt->bo);
@@ -377,8 +380,10 @@ xe_pt_insert_entry(struct xe_pt_stage_bind_walk *xe_walk, struct xe_pt *parent,
 		/* Continue building a non-connected subtree. */
 		struct iosys_map *map = &parent->bo->vmap;
 
-		if (unlikely(xe_child))
+		if (unlikely(xe_child)) {
 			parent->base.children[offset] = &xe_child->base;
+			parent->base.staging[offset] = &xe_child->base;
+		}
 
 		xe_pt_write(xe_walk->vm->xe, map, offset, pte);
 		parent->num_live++;
@@ -619,6 +624,7 @@ xe_pt_stage_bind(struct xe_tile *tile, struct xe_vma *vma,
 			.ops = &xe_pt_stage_bind_ops,
 			.shifts = xe_normal_pt_shifts,
 			.max_level = XE_PT_HIGHEST_LEVEL,
+			.staging = true,
 		},
 		.vm = xe_vma_vm(vma),
 		.tile = tile,
@@ -812,6 +818,7 @@ static const struct xe_pt_walk_ops xe_pt_zap_ptes_ops = {
 
 struct xe_pt_zap_ptes_flags {
 	bool scratch:1;
+	bool staging:1;
 };
 
 static bool __xe_pt_zap_ptes(struct xe_tile *tile, struct xe_vma *vma,
@@ -822,6 +829,7 @@ static bool __xe_pt_zap_ptes(struct xe_tile *tile, struct xe_vma *vma,
 			.ops = &xe_pt_zap_ptes_ops,
 			.shifts = xe_normal_pt_shifts,
 			.max_level = XE_PT_HIGHEST_LEVEL,
+			.staging = flags.staging,
 		},
 		.tile = tile,
 		.vm = xe_vma_vm(vma),
@@ -905,7 +913,7 @@ static void xe_pt_cancel_bind(struct xe_vma *vma,
 	}
 }
 
-static void xe_pt_commit_locks_assert(struct xe_vma *vma)
+static void xe_pt_commit_prepare_locks_assert(struct xe_vma *vma)
 {
 	struct xe_vm *vm = xe_vma_vm(vma);
 
@@ -917,6 +925,16 @@ static void xe_pt_commit_locks_assert(struct xe_vma *vma)
 	xe_vm_assert_held(vm);
 }
 
+static void xe_pt_commit_locks_assert(struct xe_vma *vma)
+{
+	struct xe_vm *vm = xe_vma_vm(vma);
+
+	xe_pt_commit_prepare_locks_assert(vma);
+
+	if (xe_vma_is_userptr(vma))
+		lockdep_assert_held_read(&vm->userptr.notifier_lock);
+}
+
 static void xe_pt_commit(struct xe_vma *vma,
 			 struct xe_vm_pgtable_update *entries,
 			 u32 num_entries, struct llist_head *deferred)
@@ -927,13 +945,17 @@ static void xe_pt_commit(struct xe_vma *vma,
 
 	for (i = 0; i < num_entries; i++) {
 		struct xe_pt *pt = entries[i].pt;
+		struct xe_pt_dir *pt_dir;
 
 		if (!pt->level)
 			continue;
 
+		pt_dir = as_xe_pt_dir(pt);
 		for (j = 0; j < entries[i].qwords; j++) {
 			struct xe_pt *oldpte = entries[i].pt_entries[j].pt;
+			int j_ = j + entries[i].ofs;
 
+			pt_dir->children[j_] = pt_dir->staging[j_];
 			xe_pt_destroy(oldpte, xe_vma_vm(vma)->flags, deferred);
 		}
 	}
@@ -945,7 +967,7 @@ static void xe_pt_abort_bind(struct xe_vma *vma,
 {
 	int i, j;
 
-	xe_pt_commit_locks_assert(vma);
+	xe_pt_commit_prepare_locks_assert(vma);
 
 	for (i = num_entries - 1; i >= 0; --i) {
 		struct xe_pt *pt = entries[i].pt;
@@ -963,7 +985,7 @@ static void xe_pt_abort_bind(struct xe_vma *vma,
 			struct xe_pt *newpte = xe_pt_entry(pt_dir, j_);
 			struct xe_pt *oldpte = entries[i].pt_entries[j].pt;
 
-			pt_dir->children[j_] = oldpte ? &oldpte->base : 0;
+			pt_dir->staging[j_] = oldpte ? &oldpte->base : 0;
 			xe_pt_destroy(newpte, xe_vma_vm(vma)->flags, NULL);
 		}
 	}
@@ -975,7 +997,7 @@ static void xe_pt_commit_prepare_bind(struct xe_vma *vma,
 {
 	u32 i, j;
 
-	xe_pt_commit_locks_assert(vma);
+	xe_pt_commit_prepare_locks_assert(vma);
 
 	for (i = 0; i < num_entries; i++) {
 		struct xe_pt *pt = entries[i].pt;
@@ -996,7 +1018,7 @@ static void xe_pt_commit_prepare_bind(struct xe_vma *vma,
 			if (xe_pt_entry(pt_dir, j_))
 				oldpte = xe_pt_entry(pt_dir, j_);
 
-			pt_dir->children[j_] = &newpte->base;
+			pt_dir->staging[j_] = &newpte->base;
 			entries[i].pt_entries[j].pt = oldpte;
 		}
 	}
@@ -1237,7 +1259,10 @@ static void
 vma_convert_to_invalidation(struct xe_tile *tile, struct xe_vma *vma,
 			    struct xe_vm_pgtable_update_ops *pt_update)
 {
-	struct xe_pt_zap_ptes_flags flags = { .scratch = true, };
+	struct xe_pt_zap_ptes_flags flags = {
+		.scratch = true,
+		.staging = true,
+	};
 	int i, j, k;
 
 	/*
@@ -1590,6 +1615,7 @@ static unsigned int xe_pt_stage_unbind(struct xe_tile *tile, struct xe_vma *vma,
 			.ops = &xe_pt_stage_unbind_ops,
 			.shifts = xe_normal_pt_shifts,
 			.max_level = XE_PT_HIGHEST_LEVEL,
+			.staging = true,
 		},
 		.tile = tile,
 		.modified_start = xe_vma_start(vma),
@@ -1631,7 +1657,7 @@ static void xe_pt_abort_unbind(struct xe_vma *vma,
 {
 	int i, j;
 
-	xe_pt_commit_locks_assert(vma);
+	xe_pt_commit_prepare_locks_assert(vma);
 
 	for (i = num_entries - 1; i >= 0; --i) {
 		struct xe_vm_pgtable_update *entry = &entries[i];
@@ -1644,7 +1670,7 @@ static void xe_pt_abort_unbind(struct xe_vma *vma,
 			continue;
 
 		for (j = entry->ofs; j < entry->ofs + entry->qwords; j++)
-			pt_dir->children[j] =
+			pt_dir->staging[j] =
 				entries[i].pt_entries[j - entry->ofs].pt ?
 				&entries[i].pt_entries[j - entry->ofs].pt->base : NULL;
 	}
@@ -1657,7 +1683,7 @@ xe_pt_commit_prepare_unbind(struct xe_vma *vma,
 {
 	int i, j;
 
-	xe_pt_commit_locks_assert(vma);
+	xe_pt_commit_prepare_locks_assert(vma);
 
 	for (i = 0; i < num_entries; ++i) {
 		struct xe_vm_pgtable_update *entry = &entries[i];
@@ -1672,7 +1698,7 @@ xe_pt_commit_prepare_unbind(struct xe_vma *vma,
 		for (j = entry->ofs; j < entry->ofs + entry->qwords; j++) {
 			entry->pt_entries[j - entry->ofs].pt =
 				xe_pt_entry(pt_dir, j);
-			pt_dir->children[j] = NULL;
+			pt_dir->staging[j] = NULL;
 		}
 	}
 }
diff --git a/drivers/gpu/drm/xe/xe_pt_walk.c b/drivers/gpu/drm/xe/xe_pt_walk.c
index b8b3d2aea492..be602a763ff3 100644
--- a/drivers/gpu/drm/xe/xe_pt_walk.c
+++ b/drivers/gpu/drm/xe/xe_pt_walk.c
@@ -74,7 +74,8 @@ int xe_pt_walk_range(struct xe_ptw *parent, unsigned int level,
 		     u64 addr, u64 end, struct xe_pt_walk *walk)
 {
 	pgoff_t offset = xe_pt_offset(addr, level, walk);
-	struct xe_ptw **entries = parent->children ? parent->children : NULL;
+	struct xe_ptw **entries = walk->staging ? (parent->staging ?: NULL) :
+		(parent->children ?: NULL);
 	const struct xe_pt_walk_ops *ops = walk->ops;
 	enum page_walk_action action;
 	struct xe_ptw *child;
diff --git a/drivers/gpu/drm/xe/xe_pt_walk.h b/drivers/gpu/drm/xe/xe_pt_walk.h
index 5ecc4d2f0f65..5c02c244f7de 100644
--- a/drivers/gpu/drm/xe/xe_pt_walk.h
+++ b/drivers/gpu/drm/xe/xe_pt_walk.h
@@ -11,12 +11,14 @@
 /**
  * struct xe_ptw - base class for driver pagetable subclassing.
  * @children: Pointer to an array of children if any.
+ * @staging: Pointer to an array of staging if any.
  *
  * Drivers could subclass this, and if it's a page-directory, typically
  * embed an array of xe_ptw pointers.
  */
 struct xe_ptw {
 	struct xe_ptw **children;
+	struct xe_ptw **staging;
 };
 
 /**
@@ -41,6 +43,8 @@ struct xe_pt_walk {
 	 * as shared pagetables.
 	 */
 	bool shared_pt_mode;
+	/** @staging: Walk staging PT structure */
+	bool staging;
 };
 
 /**
-- 
2.34.1

Re: [PATCH v2 3/3] drm/xe: Add staging tree for VM binds

[Thomas Hellström]

Hi,

On Sun, 2025-02-23 at 20:05 -0800, Matthew Brost wrote:
> Concurrent VM bind staging and zapping of PTEs from a userptr
> notifier
> do not work because the view of PTEs is not stable. VM binds cannot
> acquire the notifier lock during staging, as memory allocations are
> required. To resolve this race condition, use a staging tree for VM
> binds that is committed only under the userptr notifier lock during
> the
> final step of the bind. This ensures a consistent view of the PTEs in
> the userptr notifier.
> 
> A follow up may only use staging for VM in fault mode as this is the
> only mode in which the above race exists.
> 
> Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: <stable@vger.kernel.org>
> Fixes: e8babb280b5e ("drm/xe: Convert multiple bind ops into single
> job")
> Fixes: a708f6501c69 ("drm/xe: Update PT layer with better error
> handling")
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>

This looks even simpler than what I initially thought. Ideally I think
the staging tree would exist only under the vm lock during the multi
bind-unbind operation, but that adds code complication and execution
time compared to this solution which is more memory-hungry.

Minor comment below.

> ---
>  drivers/gpu/drm/xe/xe_pt.c      | 50 +++++++++++++++++++++++++------
> --
>  drivers/gpu/drm/xe/xe_pt_walk.c |  3 +-
>  drivers/gpu/drm/xe/xe_pt_walk.h |  4 +++
>  3 files changed, 44 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
> index add521b5c6ae..118b81cd7205 100644
> --- a/drivers/gpu/drm/xe/xe_pt.c
> +++ b/drivers/gpu/drm/xe/xe_pt.c
> @@ -28,6 +28,8 @@ struct xe_pt_dir {
>  	struct xe_pt pt;
>  	/** @children: Array of page-table child nodes */
>  	struct xe_ptw *children[XE_PDES];
> +	/** @staging: Array of page-table staging nodes */
> +	struct xe_ptw *staging[XE_PDES];
>  };
>  
>  #if IS_ENABLED(CONFIG_DRM_XE_DEBUG_VM)
> @@ -50,7 +52,7 @@ static struct xe_pt_dir *as_xe_pt_dir(struct xe_pt
> *pt)
>  
>  static struct xe_pt *xe_pt_entry(struct xe_pt_dir *pt_dir, unsigned
> int index)
>  {
> -	return container_of(pt_dir->children[index], struct xe_pt,
> base);
> +	return container_of(pt_dir->staging[index], struct xe_pt,
> base);

It looks like the only user here is with staging == true, but I'm a
little worried about future users. Perhaps include a staging bool in
the interface and assert that it is true? Or rename to
xe_pt_entry_staging()?


>  }
>  
>  static u64 __xe_pt_empty_pte(struct xe_tile *tile, struct xe_vm *vm,
> @@ -125,6 +127,7 @@ struct xe_pt *xe_pt_create(struct xe_vm *vm,
> struct xe_tile *tile,
>  	}
>  	pt->bo = bo;
>  	pt->base.children = level ? as_xe_pt_dir(pt)->children :
> NULL;
> +	pt->base.staging = level ? as_xe_pt_dir(pt)->staging : NULL;
>  
>  	if (vm->xef)
>  		xe_drm_client_add_bo(vm->xef->client, pt->bo);
> @@ -377,8 +380,10 @@ xe_pt_insert_entry(struct xe_pt_stage_bind_walk
> *xe_walk, struct xe_pt *parent,
>  		/* Continue building a non-connected subtree. */
>  		struct iosys_map *map = &parent->bo->vmap;
>  
> -		if (unlikely(xe_child))
> +		if (unlikely(xe_child)) {
>  			parent->base.children[offset] = &xe_child-
> >base;
> +			parent->base.staging[offset] = &xe_child-
> >base;
> +		}
>  
>  		xe_pt_write(xe_walk->vm->xe, map, offset, pte);
>  		parent->num_live++;
> @@ -619,6 +624,7 @@ xe_pt_stage_bind(struct xe_tile *tile, struct
> xe_vma *vma,
>  			.ops = &xe_pt_stage_bind_ops,
>  			.shifts = xe_normal_pt_shifts,
>  			.max_level = XE_PT_HIGHEST_LEVEL,
> +			.staging = true,
>  		},
>  		.vm = xe_vma_vm(vma),
>  		.tile = tile,
> @@ -812,6 +818,7 @@ static const struct xe_pt_walk_ops
> xe_pt_zap_ptes_ops = {
>  
>  struct xe_pt_zap_ptes_flags {
>  	bool scratch:1;
> +	bool staging:1;
>  };

As mentioned in the comments to the previous commit. I don't think
zapping is needed when aborting a bind.

Otherwise LGTM
/Thomas

>  
>  static bool __xe_pt_zap_ptes(struct xe_tile *tile, struct xe_vma
> *vma,
> @@ -822,6 +829,7 @@ static bool __xe_pt_zap_ptes(struct xe_tile
> *tile, struct xe_vma *vma,
>  			.ops = &xe_pt_zap_ptes_ops,
>  			.shifts = xe_normal_pt_shifts,
>  			.max_level = XE_PT_HIGHEST_LEVEL,
> +			.staging = flags.staging,
>  		},
>  		.tile = tile,
>  		.vm = xe_vma_vm(vma),
> @@ -905,7 +913,7 @@ static void xe_pt_cancel_bind(struct xe_vma *vma,
>  	}
>  }
>  
> -static void xe_pt_commit_locks_assert(struct xe_vma *vma)
> +static void xe_pt_commit_prepare_locks_assert(struct xe_vma *vma)
>  {
>  	struct xe_vm *vm = xe_vma_vm(vma);
>  
> @@ -917,6 +925,16 @@ static void xe_pt_commit_locks_assert(struct
> xe_vma *vma)
>  	xe_vm_assert_held(vm);
>  }
>  
> +static void xe_pt_commit_locks_assert(struct xe_vma *vma)
> +{
> +	struct xe_vm *vm = xe_vma_vm(vma);
> +
> +	xe_pt_commit_prepare_locks_assert(vma);
> +
> +	if (xe_vma_is_userptr(vma))
> +		lockdep_assert_held_read(&vm-
> >userptr.notifier_lock);
> +}
> +
>  static void xe_pt_commit(struct xe_vma *vma,
>  			 struct xe_vm_pgtable_update *entries,
>  			 u32 num_entries, struct llist_head
> *deferred)
> @@ -927,13 +945,17 @@ static void xe_pt_commit(struct xe_vma *vma,
>  
>  	for (i = 0; i < num_entries; i++) {
>  		struct xe_pt *pt = entries[i].pt;
> +		struct xe_pt_dir *pt_dir;
>  
>  		if (!pt->level)
>  			continue;
>  
> +		pt_dir = as_xe_pt_dir(pt);
>  		for (j = 0; j < entries[i].qwords; j++) {
>  			struct xe_pt *oldpte =
> entries[i].pt_entries[j].pt;
> +			int j_ = j + entries[i].ofs;
>  
> +			pt_dir->children[j_] = pt_dir->staging[j_];
>  			xe_pt_destroy(oldpte, xe_vma_vm(vma)->flags,
> deferred);
>  		}
>  	}
> @@ -945,7 +967,7 @@ static void xe_pt_abort_bind(struct xe_vma *vma,
>  {
>  	int i, j;
>  
> -	xe_pt_commit_locks_assert(vma);
> +	xe_pt_commit_prepare_locks_assert(vma);
>  
>  	for (i = num_entries - 1; i >= 0; --i) {
>  		struct xe_pt *pt = entries[i].pt;
> @@ -963,7 +985,7 @@ static void xe_pt_abort_bind(struct xe_vma *vma,
>  			struct xe_pt *newpte = xe_pt_entry(pt_dir,
> j_);
>  			struct xe_pt *oldpte =
> entries[i].pt_entries[j].pt;
>  
> -			pt_dir->children[j_] = oldpte ? &oldpte-
> >base : 0;
> +			pt_dir->staging[j_] = oldpte ? &oldpte->base
> : 0;
>  			xe_pt_destroy(newpte, xe_vma_vm(vma)->flags,
> NULL);
>  		}
>  	}
> @@ -975,7 +997,7 @@ static void xe_pt_commit_prepare_bind(struct
> xe_vma *vma,
>  {
>  	u32 i, j;
>  
> -	xe_pt_commit_locks_assert(vma);
> +	xe_pt_commit_prepare_locks_assert(vma);
>  
>  	for (i = 0; i < num_entries; i++) {
>  		struct xe_pt *pt = entries[i].pt;
> @@ -996,7 +1018,7 @@ static void xe_pt_commit_prepare_bind(struct
> xe_vma *vma,
>  			if (xe_pt_entry(pt_dir, j_))
>  				oldpte = xe_pt_entry(pt_dir, j_);
>  
> -			pt_dir->children[j_] = &newpte->base;
> +			pt_dir->staging[j_] = &newpte->base;
>  			entries[i].pt_entries[j].pt = oldpte;
>  		}
>  	}
> @@ -1237,7 +1259,10 @@ static void
>  vma_convert_to_invalidation(struct xe_tile *tile, struct xe_vma
> *vma,
>  			    struct xe_vm_pgtable_update_ops
> *pt_update)
>  {
> -	struct xe_pt_zap_ptes_flags flags = { .scratch = true, };
> +	struct xe_pt_zap_ptes_flags flags = {
> +		.scratch = true,
> +		.staging = true,
> +	};
>  	int i, j, k;
>  
>  	/*
> @@ -1590,6 +1615,7 @@ static unsigned int xe_pt_stage_unbind(struct
> xe_tile *tile, struct xe_vma *vma,
>  			.ops = &xe_pt_stage_unbind_ops,
>  			.shifts = xe_normal_pt_shifts,
>  			.max_level = XE_PT_HIGHEST_LEVEL,
> +			.staging = true,
>  		},
>  		.tile = tile,
>  		.modified_start = xe_vma_start(vma),
> @@ -1631,7 +1657,7 @@ static void xe_pt_abort_unbind(struct xe_vma
> *vma,
>  {
>  	int i, j;
>  
> -	xe_pt_commit_locks_assert(vma);
> +	xe_pt_commit_prepare_locks_assert(vma);
>  
>  	for (i = num_entries - 1; i >= 0; --i) {
>  		struct xe_vm_pgtable_update *entry = &entries[i];
> @@ -1644,7 +1670,7 @@ static void xe_pt_abort_unbind(struct xe_vma
> *vma,
>  			continue;
>  
>  		for (j = entry->ofs; j < entry->ofs + entry->qwords;
> j++)
> -			pt_dir->children[j] =
> +			pt_dir->staging[j] =
>  				entries[i].pt_entries[j - entry-
> >ofs].pt ?
>  				&entries[i].pt_entries[j - entry-
> >ofs].pt->base : NULL;
>  	}
> @@ -1657,7 +1683,7 @@ xe_pt_commit_prepare_unbind(struct xe_vma *vma,
>  {
>  	int i, j;
>  
> -	xe_pt_commit_locks_assert(vma);
> +	xe_pt_commit_prepare_locks_assert(vma);
>  
>  	for (i = 0; i < num_entries; ++i) {
>  		struct xe_vm_pgtable_update *entry = &entries[i];
> @@ -1672,7 +1698,7 @@ xe_pt_commit_prepare_unbind(struct xe_vma *vma,
>  		for (j = entry->ofs; j < entry->ofs + entry->qwords;
> j++) {
>  			entry->pt_entries[j - entry->ofs].pt =
>  				xe_pt_entry(pt_dir, j);
> -			pt_dir->children[j] = NULL;
> +			pt_dir->staging[j] = NULL;
>  		}
>  	}
>  }
> diff --git a/drivers/gpu/drm/xe/xe_pt_walk.c
> b/drivers/gpu/drm/xe/xe_pt_walk.c
> index b8b3d2aea492..be602a763ff3 100644
> --- a/drivers/gpu/drm/xe/xe_pt_walk.c
> +++ b/drivers/gpu/drm/xe/xe_pt_walk.c
> @@ -74,7 +74,8 @@ int xe_pt_walk_range(struct xe_ptw *parent,
> unsigned int level,
>  		     u64 addr, u64 end, struct xe_pt_walk *walk)
>  {
>  	pgoff_t offset = xe_pt_offset(addr, level, walk);
> -	struct xe_ptw **entries = parent->children ? parent-
> >children : NULL;
> +	struct xe_ptw **entries = walk->staging ? (parent->staging
> ?: NULL) :
> +		(parent->children ?: NULL);
>  	const struct xe_pt_walk_ops *ops = walk->ops;
>  	enum page_walk_action action;
>  	struct xe_ptw *child;
> diff --git a/drivers/gpu/drm/xe/xe_pt_walk.h
> b/drivers/gpu/drm/xe/xe_pt_walk.h
> index 5ecc4d2f0f65..5c02c244f7de 100644
> --- a/drivers/gpu/drm/xe/xe_pt_walk.h
> +++ b/drivers/gpu/drm/xe/xe_pt_walk.h
> @@ -11,12 +11,14 @@
>  /**
>   * struct xe_ptw - base class for driver pagetable subclassing.
>   * @children: Pointer to an array of children if any.
> + * @staging: Pointer to an array of staging if any.
>   *
>   * Drivers could subclass this, and if it's a page-directory,
> typically
>   * embed an array of xe_ptw pointers.
>   */
>  struct xe_ptw {
>  	struct xe_ptw **children;
> +	struct xe_ptw **staging;
>  };
>  
>  /**
> @@ -41,6 +43,8 @@ struct xe_pt_walk {
>  	 * as shared pagetables.
>  	 */
>  	bool shared_pt_mode;
> +	/** @staging: Walk staging PT structure */
> +	bool staging;
>  };
>  
>  /**

Re: [PATCH v2 3/3] drm/xe: Add staging tree for VM binds

[Matthew Brost]

On Mon, Feb 24, 2025 at 10:22:37AM +0100, Thomas Hellström wrote:
> Hi,
> 
> On Sun, 2025-02-23 at 20:05 -0800, Matthew Brost wrote:
> > Concurrent VM bind staging and zapping of PTEs from a userptr
> > notifier
> > do not work because the view of PTEs is not stable. VM binds cannot
> > acquire the notifier lock during staging, as memory allocations are
> > required. To resolve this race condition, use a staging tree for VM
> > binds that is committed only under the userptr notifier lock during
> > the
> > final step of the bind. This ensures a consistent view of the PTEs in
> > the userptr notifier.
> > 
> > A follow up may only use staging for VM in fault mode as this is the
> > only mode in which the above race exists.
> > 
> > Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > Cc: <stable@vger.kernel.org>
> > Fixes: e8babb280b5e ("drm/xe: Convert multiple bind ops into single
> > job")
> > Fixes: a708f6501c69 ("drm/xe: Update PT layer with better error
> > handling")
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> 
> This looks even simpler than what I initially thought. Ideally I think

Was pleasantly by how simple this was.

> the staging tree would exist only under the vm lock during the multi
> bind-unbind operation, but that adds code complication and execution
> time compared to this solution which is more memory-hungry.
>

It does take a bit more memory but I doubt that is a concern. We only
allocate an extra page of memory for each PDE which is pretty minor
considering the smallest PDE is still mapping 1G of memory. As I mention
in the commit message we could even drop the staging for non faulting
VMs too.
 
> Minor comment below.
> 
> > ---
> >  drivers/gpu/drm/xe/xe_pt.c      | 50 +++++++++++++++++++++++++------
> > --
> >  drivers/gpu/drm/xe/xe_pt_walk.c |  3 +-
> >  drivers/gpu/drm/xe/xe_pt_walk.h |  4 +++
> >  3 files changed, 44 insertions(+), 13 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
> > index add521b5c6ae..118b81cd7205 100644
> > --- a/drivers/gpu/drm/xe/xe_pt.c
> > +++ b/drivers/gpu/drm/xe/xe_pt.c
> > @@ -28,6 +28,8 @@ struct xe_pt_dir {
> >  	struct xe_pt pt;
> >  	/** @children: Array of page-table child nodes */
> >  	struct xe_ptw *children[XE_PDES];
> > +	/** @staging: Array of page-table staging nodes */
> > +	struct xe_ptw *staging[XE_PDES];
> >  };
> >  
> >  #if IS_ENABLED(CONFIG_DRM_XE_DEBUG_VM)
> > @@ -50,7 +52,7 @@ static struct xe_pt_dir *as_xe_pt_dir(struct xe_pt
> > *pt)
> >  
> >  static struct xe_pt *xe_pt_entry(struct xe_pt_dir *pt_dir, unsigned
> > int index)
> >  {
> > -	return container_of(pt_dir->children[index], struct xe_pt,
> > base);
> > +	return container_of(pt_dir->staging[index], struct xe_pt,
> > base);
> 
> It looks like the only user here is with staging == true, but I'm a
> little worried about future users. Perhaps include a staging bool in
> the interface and assert that it is true? Or rename to
> xe_pt_entry_staging()?
> 

I had a bool originally but found that xe_pt_entry is only called during
the staging steps so dropped it. Can rename to xe_pt_entry_staging for
clarity. 

> 
> >  }
> >  
> >  static u64 __xe_pt_empty_pte(struct xe_tile *tile, struct xe_vm *vm,
> > @@ -125,6 +127,7 @@ struct xe_pt *xe_pt_create(struct xe_vm *vm,
> > struct xe_tile *tile,
> >  	}
> >  	pt->bo = bo;
> >  	pt->base.children = level ? as_xe_pt_dir(pt)->children :
> > NULL;
> > +	pt->base.staging = level ? as_xe_pt_dir(pt)->staging : NULL;
> >  
> >  	if (vm->xef)
> >  		xe_drm_client_add_bo(vm->xef->client, pt->bo);
> > @@ -377,8 +380,10 @@ xe_pt_insert_entry(struct xe_pt_stage_bind_walk
> > *xe_walk, struct xe_pt *parent,
> >  		/* Continue building a non-connected subtree. */
> >  		struct iosys_map *map = &parent->bo->vmap;
> >  
> > -		if (unlikely(xe_child))
> > +		if (unlikely(xe_child)) {
> >  			parent->base.children[offset] = &xe_child-
> > >base;
> > +			parent->base.staging[offset] = &xe_child-
> > >base;
> > +		}
> >  
> >  		xe_pt_write(xe_walk->vm->xe, map, offset, pte);
> >  		parent->num_live++;
> > @@ -619,6 +624,7 @@ xe_pt_stage_bind(struct xe_tile *tile, struct
> > xe_vma *vma,
> >  			.ops = &xe_pt_stage_bind_ops,
> >  			.shifts = xe_normal_pt_shifts,
> >  			.max_level = XE_PT_HIGHEST_LEVEL,
> > +			.staging = true,
> >  		},
> >  		.vm = xe_vma_vm(vma),
> >  		.tile = tile,
> > @@ -812,6 +818,7 @@ static const struct xe_pt_walk_ops
> > xe_pt_zap_ptes_ops = {
> >  
> >  struct xe_pt_zap_ptes_flags {
> >  	bool scratch:1;
> > +	bool staging:1;
> >  };
> 
> As mentioned in the comments to the previous commit. I don't think
> zapping is needed when aborting a bind.
> 

Let me reply there as I think there is a bit of confusion still.

Matt

> Otherwise LGTM
> /Thomas
> 
> >  
> >  static bool __xe_pt_zap_ptes(struct xe_tile *tile, struct xe_vma
> > *vma,
> > @@ -822,6 +829,7 @@ static bool __xe_pt_zap_ptes(struct xe_tile
> > *tile, struct xe_vma *vma,
> >  			.ops = &xe_pt_zap_ptes_ops,
> >  			.shifts = xe_normal_pt_shifts,
> >  			.max_level = XE_PT_HIGHEST_LEVEL,
> > +			.staging = flags.staging,
> >  		},
> >  		.tile = tile,
> >  		.vm = xe_vma_vm(vma),
> > @@ -905,7 +913,7 @@ static void xe_pt_cancel_bind(struct xe_vma *vma,
> >  	}
> >  }
> >  
> > -static void xe_pt_commit_locks_assert(struct xe_vma *vma)
> > +static void xe_pt_commit_prepare_locks_assert(struct xe_vma *vma)
> >  {
> >  	struct xe_vm *vm = xe_vma_vm(vma);
> >  
> > @@ -917,6 +925,16 @@ static void xe_pt_commit_locks_assert(struct
> > xe_vma *vma)
> >  	xe_vm_assert_held(vm);
> >  }
> >  
> > +static void xe_pt_commit_locks_assert(struct xe_vma *vma)
> > +{
> > +	struct xe_vm *vm = xe_vma_vm(vma);
> > +
> > +	xe_pt_commit_prepare_locks_assert(vma);
> > +
> > +	if (xe_vma_is_userptr(vma))
> > +		lockdep_assert_held_read(&vm-
> > >userptr.notifier_lock);
> > +}
> > +
> >  static void xe_pt_commit(struct xe_vma *vma,
> >  			 struct xe_vm_pgtable_update *entries,
> >  			 u32 num_entries, struct llist_head
> > *deferred)
> > @@ -927,13 +945,17 @@ static void xe_pt_commit(struct xe_vma *vma,
> >  
> >  	for (i = 0; i < num_entries; i++) {
> >  		struct xe_pt *pt = entries[i].pt;
> > +		struct xe_pt_dir *pt_dir;
> >  
> >  		if (!pt->level)
> >  			continue;
> >  
> > +		pt_dir = as_xe_pt_dir(pt);
> >  		for (j = 0; j < entries[i].qwords; j++) {
> >  			struct xe_pt *oldpte =
> > entries[i].pt_entries[j].pt;
> > +			int j_ = j + entries[i].ofs;
> >  
> > +			pt_dir->children[j_] = pt_dir->staging[j_];
> >  			xe_pt_destroy(oldpte, xe_vma_vm(vma)->flags,
> > deferred);
> >  		}
> >  	}
> > @@ -945,7 +967,7 @@ static void xe_pt_abort_bind(struct xe_vma *vma,
> >  {
> >  	int i, j;
> >  
> > -	xe_pt_commit_locks_assert(vma);
> > +	xe_pt_commit_prepare_locks_assert(vma);
> >  
> >  	for (i = num_entries - 1; i >= 0; --i) {
> >  		struct xe_pt *pt = entries[i].pt;
> > @@ -963,7 +985,7 @@ static void xe_pt_abort_bind(struct xe_vma *vma,
> >  			struct xe_pt *newpte = xe_pt_entry(pt_dir,
> > j_);
> >  			struct xe_pt *oldpte =
> > entries[i].pt_entries[j].pt;
> >  
> > -			pt_dir->children[j_] = oldpte ? &oldpte-
> > >base : 0;
> > +			pt_dir->staging[j_] = oldpte ? &oldpte->base
> > : 0;
> >  			xe_pt_destroy(newpte, xe_vma_vm(vma)->flags,
> > NULL);
> >  		}
> >  	}
> > @@ -975,7 +997,7 @@ static void xe_pt_commit_prepare_bind(struct
> > xe_vma *vma,
> >  {
> >  	u32 i, j;
> >  
> > -	xe_pt_commit_locks_assert(vma);
> > +	xe_pt_commit_prepare_locks_assert(vma);
> >  
> >  	for (i = 0; i < num_entries; i++) {
> >  		struct xe_pt *pt = entries[i].pt;
> > @@ -996,7 +1018,7 @@ static void xe_pt_commit_prepare_bind(struct
> > xe_vma *vma,
> >  			if (xe_pt_entry(pt_dir, j_))
> >  				oldpte = xe_pt_entry(pt_dir, j_);
> >  
> > -			pt_dir->children[j_] = &newpte->base;
> > +			pt_dir->staging[j_] = &newpte->base;
> >  			entries[i].pt_entries[j].pt = oldpte;
> >  		}
> >  	}
> > @@ -1237,7 +1259,10 @@ static void
> >  vma_convert_to_invalidation(struct xe_tile *tile, struct xe_vma
> > *vma,
> >  			    struct xe_vm_pgtable_update_ops
> > *pt_update)
> >  {
> > -	struct xe_pt_zap_ptes_flags flags = { .scratch = true, };
> > +	struct xe_pt_zap_ptes_flags flags = {
> > +		.scratch = true,
> > +		.staging = true,
> > +	};
> >  	int i, j, k;
> >  
> >  	/*
> > @@ -1590,6 +1615,7 @@ static unsigned int xe_pt_stage_unbind(struct
> > xe_tile *tile, struct xe_vma *vma,
> >  			.ops = &xe_pt_stage_unbind_ops,
> >  			.shifts = xe_normal_pt_shifts,
> >  			.max_level = XE_PT_HIGHEST_LEVEL,
> > +			.staging = true,
> >  		},
> >  		.tile = tile,
> >  		.modified_start = xe_vma_start(vma),
> > @@ -1631,7 +1657,7 @@ static void xe_pt_abort_unbind(struct xe_vma
> > *vma,
> >  {
> >  	int i, j;
> >  
> > -	xe_pt_commit_locks_assert(vma);
> > +	xe_pt_commit_prepare_locks_assert(vma);
> >  
> >  	for (i = num_entries - 1; i >= 0; --i) {
> >  		struct xe_vm_pgtable_update *entry = &entries[i];
> > @@ -1644,7 +1670,7 @@ static void xe_pt_abort_unbind(struct xe_vma
> > *vma,
> >  			continue;
> >  
> >  		for (j = entry->ofs; j < entry->ofs + entry->qwords;
> > j++)
> > -			pt_dir->children[j] =
> > +			pt_dir->staging[j] =
> >  				entries[i].pt_entries[j - entry-
> > >ofs].pt ?
> >  				&entries[i].pt_entries[j - entry-
> > >ofs].pt->base : NULL;
> >  	}
> > @@ -1657,7 +1683,7 @@ xe_pt_commit_prepare_unbind(struct xe_vma *vma,
> >  {
> >  	int i, j;
> >  
> > -	xe_pt_commit_locks_assert(vma);
> > +	xe_pt_commit_prepare_locks_assert(vma);
> >  
> >  	for (i = 0; i < num_entries; ++i) {
> >  		struct xe_vm_pgtable_update *entry = &entries[i];
> > @@ -1672,7 +1698,7 @@ xe_pt_commit_prepare_unbind(struct xe_vma *vma,
> >  		for (j = entry->ofs; j < entry->ofs + entry->qwords;
> > j++) {
> >  			entry->pt_entries[j - entry->ofs].pt =
> >  				xe_pt_entry(pt_dir, j);
> > -			pt_dir->children[j] = NULL;
> > +			pt_dir->staging[j] = NULL;
> >  		}
> >  	}
> >  }
> > diff --git a/drivers/gpu/drm/xe/xe_pt_walk.c
> > b/drivers/gpu/drm/xe/xe_pt_walk.c
> > index b8b3d2aea492..be602a763ff3 100644
> > --- a/drivers/gpu/drm/xe/xe_pt_walk.c
> > +++ b/drivers/gpu/drm/xe/xe_pt_walk.c
> > @@ -74,7 +74,8 @@ int xe_pt_walk_range(struct xe_ptw *parent,
> > unsigned int level,
> >  		     u64 addr, u64 end, struct xe_pt_walk *walk)
> >  {
> >  	pgoff_t offset = xe_pt_offset(addr, level, walk);
> > -	struct xe_ptw **entries = parent->children ? parent-
> > >children : NULL;
> > +	struct xe_ptw **entries = walk->staging ? (parent->staging
> > ?: NULL) :
> > +		(parent->children ?: NULL);
> >  	const struct xe_pt_walk_ops *ops = walk->ops;
> >  	enum page_walk_action action;
> >  	struct xe_ptw *child;
> > diff --git a/drivers/gpu/drm/xe/xe_pt_walk.h
> > b/drivers/gpu/drm/xe/xe_pt_walk.h
> > index 5ecc4d2f0f65..5c02c244f7de 100644
> > --- a/drivers/gpu/drm/xe/xe_pt_walk.h
> > +++ b/drivers/gpu/drm/xe/xe_pt_walk.h
> > @@ -11,12 +11,14 @@
> >  /**
> >   * struct xe_ptw - base class for driver pagetable subclassing.
> >   * @children: Pointer to an array of children if any.
> > + * @staging: Pointer to an array of staging if any.
> >   *
> >   * Drivers could subclass this, and if it's a page-directory,
> > typically
> >   * embed an array of xe_ptw pointers.
> >   */
> >  struct xe_ptw {
> >  	struct xe_ptw **children;
> > +	struct xe_ptw **staging;
> >  };
> >  
> >  /**
> > @@ -41,6 +43,8 @@ struct xe_pt_walk {
> >  	 * as shared pagetables.
> >  	 */
> >  	bool shared_pt_mode;
> > +	/** @staging: Walk staging PT structure */
> > +	bool staging;
> >  };
> >  
> >  /**
> 

✗ CI.Patch_applied: failure for Userptr fixes

[Patchwork]

== Series Details ==

Series: Userptr fixes
URL   : https://patchwork.freedesktop.org/series/145321/
State : failure

== Summary ==

=== Applying kernel patches on branch 'drm-tip' with base: ===
Base commit: a5a9504217e2 drm-tip: 2025y-02m-24d-16h-04m-10s UTC integration manifest
=== git am output follows ===
error: patch failed: drivers/gpu/drm/xe/xe_vm.c:681
error: drivers/gpu/drm/xe/xe_vm.c: patch does not apply
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Applying: drm/xe/userptr: fix EFAULT handling
Patch failed at 0001 drm/xe/userptr: fix EFAULT handling
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".