drm/xe/pt: Reset current_op in xe_pt_update_ops_init()

xe_pt_update_ops_init() fails to reset current_op to 0. On the
vm_bind path, ops_execute() calls xe_pt_update_ops_prepare() inside
the xe_validation_guard() / drm_exec_until_all_locked() loop. When
that loop retries due to lock contention or OOM eviction
(drm_exec_retry_on_contention() / xe_validation_retry_on_oom()),
xe_pt_update_ops_prepare() runs again on the same vops, and each
call to bind_op_prepare() increments current_op without resetting it.

After N retries current_op exceeds the array size allocated by
xe_vma_ops_alloc(), causing an out-of-bounds write into
SLUB-poisoned memory and a subsequent UAF crash in
xe_migrate_update_pgtables_cpu() when reading the corrupted pt_op->bind.

Also reset needs_svm_lock and needs_invalidation which are derived in
the same prepare pass and would otherwise cause wrong migrate ops
selection and redundant TLB invalidation on retry.

Fix this by resetting current_op, needs_svm_lock and needs_invalidation
in xe_pt_update_ops_init().

v2 (Matt):
   - Add details in commit message.
   - Add Fixes tag and Cc to stable@vger.kernel.org

Fixes: e8babb2 ("drm/xe: Convert multiple bind ops into single job")
Suggested-by: Matthew Auld <matthew.auld@intel.com>
Cc: stable@vger.kernel.org
Assisted-by: GitHub-Copilot:claude-sonnet-4.6
Signed-off-by: Zongyao Bai <zongyao.bai@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260714232433.2737533-1-zongyao.bai@intel.com
(cherry picked from commit 0460455)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Author: BailyBai

drivers/gpu/drm/xe/xe_pt.c

@@ -2365,8 +2365,11 @@ static void
 xe_pt_update_ops_init(struct xe_vm_pgtable_update_ops *pt_update_ops)
 {
 	init_llist_head(&pt_update_ops->deferred);
+	pt_update_ops->current_op = 0;
 	pt_update_ops->start = ~0x0ull;
 	pt_update_ops->last = 0x0ull;
+	pt_update_ops->needs_svm_lock = false;
+	pt_update_ops->needs_invalidation = false;
 	xe_page_reclaim_list_init(&pt_update_ops->prl);
 }