[PATCH] drm/xe: Fix slab-out-of-bounds on PT update ops retry

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

xe_pt_update_ops_prepare() calls xe_pt_update_ops_init() at the start of
each invocation to reset per-attempt state, but current_op was not
included in that reset. When vm_bind_ioctl_ops_execute() retries due to
ww-mutex contention (drm_exec_retry_on_contention), ops_execute() calls
xe_pt_update_ops_prepare() again. The second call walks the same op list
and fills ops[] starting from current_op, which still holds the value
from the first attempt. This indexes past the end of the ops array
allocated by xe_vma_ops_alloc(), whose size was computed for a single
pass.

KASAN reported:
  BUG: KASAN: slab-out-of-bounds in bind_op_prepare+0x89c/0xae0 [xe]
  Write of size 8 at addr ffff88812e72bae8 by task xe_evict/2848
  [...]
  bind_op_prepare+0x89c/0xae0 [xe]
  xe_pt_update_ops_prepare+0xbd0/0x1570 [xe]
  ops_execute+0x3ae/0x2030 [xe]
  vm_bind_ioctl_ops_execute+0x4d5/0xed0 [xe]

The write lands at ops[1].vma (offset 360 into the second element of a
one-element 384-byte allocation) because entries[] is exactly 360 bytes
and current_op was 1 at the start of the retried prepare pass.

Fix by resetting current_op to 0 in xe_pt_update_ops_init().

Fixes: e8babb280b5e ("drm/xe: Convert multiple bind ops into single job")
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: <stable@vger.kernel.org> # v6.12+
Assisted-by: GitHub Copilot:claude-sonnet-4.6
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 drivers/gpu/drm/xe/xe_pt.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
index 8e5f4f0dea3f..3607cd57fc4c 100644
--- a/drivers/gpu/drm/xe/xe_pt.c
+++ b/drivers/gpu/drm/xe/xe_pt.c
@@ -2291,6 +2291,7 @@ xe_pt_update_ops_init(struct xe_vm_pgtable_update_ops *pt_update_ops)
 	init_llist_head(&pt_update_ops->deferred);
 	pt_update_ops->start = ~0x0ull;
 	pt_update_ops->last = 0x0ull;
+	pt_update_ops->current_op = 0;
 	xe_page_reclaim_list_init(&pt_update_ops->prl);
 }
 
-- 
2.53.0