drm/xe: Fix fault on fd close after unbind

If userspace holds an fd open, unbinds the device and then closes it,
the driver shouldn't try to access the hardware. Protect it by using
drm_dev_enter()/drm_dev_exit(). This fixes the following page fault:

<6> [IGT] xe_wedged: exiting, ret=98
<1> BUG: unable to handle page fault for address: ffffc901bc5e508c
<1> #PF: supervisor read access in kernel mode
<1> #PF: error_code(0x0000) - not-present page
...
<4> xe_lrc_update_timestamp+0x1c/0xd0 [xe]
<4> xe_exec_queue_update_run_ticks+0x50/0xb0 [xe]
<4> xe_exec_queue_fini+0x16/0xb0 [xe]
<4> __guc_exec_queue_fini_async+0xc4/0x190 [xe]
<4> guc_exec_queue_fini_async+0xa0/0xe0 [xe]
<4> guc_exec_queue_fini+0x23/0x40 [xe]
<4> xe_exec_queue_destroy+0xb3/0xf0 [xe]
<4> xe_file_close+0xd4/0x1a0 [xe]
<4> drm_file_free+0x210/0x280 [drm]
<4> drm_close_helper.isra.0+0x6d/0x80 [drm]
<4> drm_release_noglobal+0x20/0x90 [drm]

Fixes: 514447a12190 ("drm/xe: Stop accumulating LRC timestamp on job_free")
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3421
Reviewed-by: Umesh Nerlige Ramappa <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Lucas De Marchi <[e-mail]>
(cherry picked from commit 4ca1fd418338d4d135428a0eb1e16e3b3ce17ee8)
Signed-off-by: Thomas Hellström <[e-mail]>

drivers/gpu/drm/xe/xe_exec_queue.c

···
 #include <linux/nospec.h>
 
 #include <drm/drm_device.h>
+#include <drm/drm_drv.h>
 #include <drm/drm_file.h>
 #include <uapi/drm/xe_drm.h>
 
···
  */
 void xe_exec_queue_update_run_ticks(struct xe_exec_queue *q)
 {
+	struct xe_device *xe = gt_to_xe(q->gt);
 	struct xe_file *xef;
 	struct xe_lrc *lrc;
 	u32 old_ts, new_ts;
+	int idx;
 
 	/*
 	 * Jobs that are run during driver load may use an exec_queue, but are
···
 	 * for kernel specific work.
 	 */
 	if (!q->vm || !q->vm->xef)
+		return;
+
+	/* Synchronize with unbind while holding the xe file open */
+	if (!drm_dev_enter(&xe->drm, &idx))
 		return;
 
 	xef = q->vm->xef;
···
 	lrc = q->lrc[0];
 	new_ts = xe_lrc_update_timestamp(lrc, &old_ts);
 	xef->run_ticks[q->class] += (new_ts - old_ts) * q->width;
+
+	drm_dev_exit(idx);
 }
 
 /**