[PATCH v2] vhost-scsi: flush backend after device ioctls

vhost-scsi translates guest response descriptors into userspace iovecs
when commands are submitted.  Target-core completes those commands
asynchronously, so VHOST_SET_MEM_TABLE can replace the memory table while
an in-flight command still retains response iovecs translated through the
old table.

If the old mapping is reused after VHOST_SET_MEM_TABLE returns, command
completion can write the response to an unrelated userspace object.

Flush the vhost-scsi backend after vhost_dev_ioctl() handles a device
ioctl.  This waits for in-flight commands that can still use the old
response iovecs before the ioctl returns.

Signed-off-by: Jia Jia <[email protected]>
---
Changes in v2:
- Shorten the changelog and remove investigation details.

 drivers/vhost/scsi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 9a1253b9d8c5..c3e8f1a0b2d4 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -2424,10 +2424,11 @@ vhost_scsi_ioctl(struct file *f, unsigned int ioctl, unsigned long arg)
 	default:
 		mutex_lock(&vs->dev.mutex);
 		r = vhost_dev_ioctl(&vs->dev, ioctl, argp);
-		/* TODO: flush backend after dev ioctl. */
 		if (r == -ENOIOCTLCMD)
 			r = vhost_vring_ioctl(&vs->dev, ioctl, argp);
+		else
+			vhost_scsi_flush(vs);
 		mutex_unlock(&vs->dev.mutex);
 		return r;
 	}
 }
-- 
2.43.0