[PATCH 13/13] drm/xe: Block BO VM access when device I/O is unavailable

[Arvind Yadav <arvind.yadav@intel.com>]

xe_bo_vm_access() may acquire a runtime PM reference and access a BO
during PCI error recovery, after a permanent wedge or during device
unplug.

Return -EIO when device I/O is blocked. Use drm_dev_enter() to protect
against concurrent unplug and keep that protection until the runtime PM
reference has been released.

Use the same SRCU domain as CPU faults so wedge isolation waits for a BO
access that started before the wedge.

Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
---
 drivers/gpu/drm/xe/xe_bo.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index 1eabece56f6c..717d318c7072 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -2245,9 +2245,25 @@ static int xe_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
 	struct ttm_buffer_object *ttm_bo = vma->vm_private_data;
 	struct xe_bo *bo = ttm_to_xe_bo(ttm_bo);
 	struct xe_device *xe = xe_bo_device(bo);
+	int idx, srcu_idx, ret = -EIO;
 
-	guard(xe_pm_runtime)(xe);
-	return ttm_bo_vm_access(vma, addr, buf, len, write);
+	srcu_idx = srcu_read_lock(&xe->mem_access.vram_userfault.srcu);
+
+	if (xe_device_io_blocked(xe) || !drm_dev_enter(&xe->drm, &idx))
+		goto out_srcu;
+
+	/*
+	 * Keep the drm_dev_enter() protection until the runtime PM
+	 * reference has been released.
+	 */
+	scoped_guard(xe_pm_runtime, xe)
+		ret = ttm_bo_vm_access(vma, addr, buf, len, write);
+
+	drm_dev_exit(idx);
+
+out_srcu:
+	srcu_read_unlock(&xe->mem_access.vram_userfault.srcu, srcu_idx);
+	return ret;
 }
 
 /**
-- 
2.43.0