[PATCH v4 1/3] vhost: add helper to clear device IOTLB

[Jia Jia <physicalmtea@gmail.com>]

The device IOTLB is shared by vhost backends, but clearing it requires
dropping each virtqueue's IOTLB pointer and metadata cache before the
old table is freed. Add a common helper for this teardown sequence so
backend-specific feature code only needs to decide when the table must
be cleared.

The caller must hold the device mutex. The helper does not update
acked_features; backends continue to update that state in their own
virtqueue loops.

Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/vhost/vhost.c | 24 ++++++++++++++++++++++++
 drivers/vhost/vhost.h |  1 +
 2 files changed, 25 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 269efad90369..7eaa61d9ceeb 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2283,6 +2283,30 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 }
 EXPORT_SYMBOL_GPL(vhost_vring_ioctl);
 
+/* Caller must hold the device mutex. */
+void vhost_clear_device_iotlb(struct vhost_dev *d)
+{
+	struct vhost_iotlb *iotlb;
+	int i;
+
+	iotlb = d->iotlb;
+	d->iotlb = NULL;
+
+	for (i = 0; i < d->nvqs; ++i) {
+		struct vhost_virtqueue *vq = d->vqs[i];
+
+		mutex_lock(&vq->mutex);
+		vq->iotlb = NULL;
+		__vhost_vq_meta_reset(vq);
+		mutex_unlock(&vq->mutex);
+	}
+
+	vhost_clear_msg(d);
+	vhost_iotlb_free(iotlb);
+	wake_up_interruptible_poll(&d->wait, EPOLLIN | EPOLLRDNORM);
+}
+EXPORT_SYMBOL_GPL(vhost_clear_device_iotlb);
+
 int vhost_init_device_iotlb(struct vhost_dev *d)
 {
 	struct vhost_iotlb *niotlb, *oiotlb;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 0192ade6e749..3c75e8089373 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -277,6 +277,7 @@ ssize_t vhost_chr_read_iter(struct vhost_dev *dev, struct iov_iter *to,
 			    int noblock);
 ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
 			     struct iov_iter *from);
+void vhost_clear_device_iotlb(struct vhost_dev *d);
 int vhost_init_device_iotlb(struct vhost_dev *d);
 
 void vhost_iotlb_map_free(struct vhost_iotlb *iotlb,
-- 
2.34.1