vhost: avoid backend flush on vring ops

vring changes already do a flush internally where appropriate, so we do
not need a second flush.

It's currently not very expensive but a follow-up patch makes flush more
heavy-weight, so remove the extra flush here to avoid regressing
performance if call or kick fds are changed on data path.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/net.c

@@ -942,8 +942,11 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
 		return vhost_net_reset_owner(n);
 	default:
 		mutex_lock(&n->dev.mutex);
-		r = vhost_dev_ioctl(&n->dev, ioctl, arg);
-		vhost_net_flush(n);
+		r = vhost_dev_ioctl(&n->dev, ioctl, argp);
+		if (r == -ENOIOCTLCMD)
+			r = vhost_vring_ioctl(&n->dev, ioctl, argp);
+		else
+			vhost_net_flush(n);
 		mutex_unlock(&n->dev.mutex);
 		return r;
 	}

drivers/vhost/tcm_vhost.c

@@ -970,7 +970,10 @@ static long vhost_scsi_ioctl(struct file *f, unsigned int ioctl,
 		return vhost_scsi_set_features(vs, features);
 	default:
 		mutex_lock(&vs->dev.mutex);
-		r = vhost_dev_ioctl(&vs->dev, ioctl, arg);
+		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);
 		mutex_unlock(&vs->dev.mutex);
 		return r;
 	}

drivers/vhost/vhost.c

@@ -607,7 +607,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 	return 0;
 }
 
-static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
+long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
 {
 	struct file *eventfp, *filep = NULL;
 	bool pollstart = false, pollstop = false;
@@ -802,9 +802,8 @@ static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
 }
 
 /* Caller must have device mutex */
-long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
+long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 {
-	void __user *argp = (void __user *)arg;
 	struct file *eventfp, *filep = NULL;
 	struct eventfd_ctx *ctx = NULL;
 	u64 p;
@@ -875,7 +874,7 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
 			fput(filep);
 		break;
 	default:
-		r = vhost_set_vring(d, ioctl, argp);
+		r = -ENOIOCTLCMD;
 		break;
 	}
 done:

drivers/vhost/vhost.h

@@ -164,7 +164,8 @@ long vhost_dev_check_owner(struct vhost_dev *);
 long vhost_dev_reset_owner(struct vhost_dev *);
 void vhost_dev_cleanup(struct vhost_dev *, bool locked);
 void vhost_dev_stop(struct vhost_dev *);
-long vhost_dev_ioctl(struct vhost_dev *, unsigned int ioctl, unsigned long arg);
+long vhost_dev_ioctl(struct vhost_dev *, unsigned int ioctl, void __user *argp);
+long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp);
 int vhost_vq_access_ok(struct vhost_virtqueue *vq);
 int vhost_log_access_ok(struct vhost_dev *);