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

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 <redacted>
---
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