Re: [PATCH v4 2/3] vhost/vsock: discard IOTLB when ACCESS_PLATFORM is cleared

[Stefano Garzarella <sgarzare@redhat.com>]

On Fri, Aug 14, 2026 at 03:29:02PM +0800, Jia Jia wrote:
>vhost_vsock_set_features() leaves the device IOTLB attached when
>userspace clears VIRTIO_F_ACCESS_PLATFORM. Descriptors can therefore
>continue to use translations installed before the feature change,
>including HVAs made stale by a later memory table update.
>
>Use the common vhost helper to detach the device IOTLB before
>acknowledging a feature mask without ACCESS_PLATFORM. The helper clears
>each virtqueue's IOTLB pointer and metadata cache under its mutex, then
>frees the old IOTLB after all virtqueues have dropped their references.
>
>Fixes: e13a6915a03f ("vhost/vsock: add IOTLB API support")
>Suggested-by: Michael S. Tsirkin <mst@redhat.com>
>Signed-off-by: Jia Jia <physicalmtea@gmail.com>
>---
> drivers/vhost/vsock.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
>diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>index 9aaab6bb8061..b69c260eaeff 100644
>--- a/drivers/vhost/vsock.c
>+++ b/drivers/vhost/vsock.c
>@@ -863,7 +863,11 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
> 	if ((features & (1 << VHOST_F_LOG_ALL)) &&
> 	    !vhost_log_access_ok(&vsock->dev)) {
> 		goto err;
> 	}
>
>+	if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)) &&
>+	    vsock->dev.iotlb)
>+		vhost_clear_device_iotlb(&vsock->dev);
>+

Why checking the feature again instead of adding an `else if` in the 
already existing check?

I mean this...

> 	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
> 		if (vhost_init_device_iotlb(&vsock->dev))
> 			goto err;
	} else if (vsock->dev.iotlb) {
		vhost_clear_device_iotlb(&vsock->dev);
	}

>-- 2.34.1
>