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

[Stefano Garzarella <sgarzare@redhat.com>]

On Fri, Aug 14, 2026 at 03:29:01PM +0800, Jia Jia wrote:
>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;

Should we move the check of `d->iotlb` here? so the callers doesn't need 
to access to an internal details.

Stefano

>+
>+	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
>