[PATCH v2 1/2] vhost/vsock: discard IOTLB when ACCESS_PLATFORM is cleared

[Jia Jia <physicalmtea@gmail.com>]

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.

Detach the IOTLB before acknowledging a feature mask without
ACCESS_PLATFORM. Hold all virtqueue mutexes in index order while clearing
the device and virtqueue IOTLB pointers, resetting metadata caches, and
updating the acknowledged features. This prevents a kick handler from
observing a mixed translation state.

Free the old IOTLB after releasing the virtqueue mutexes. Also drop
the old IOTLB miss messages and wake readers now that the device no
longer accepts IOTLB updates.

Fixes: e13a6915a03f ("vhost/vsock: add IOTLB API support")
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/vhost/vsock.c | 43 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 38 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 9aaab6bb8061..562b9e139a76 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -851,6 +851,34 @@ static int vhost_vsock_set_cid(struct vhost_vsock *vsock, u64 guest_cid)
 	return 0;
 }
 
+/* Caller must hold the device mutex. */
+static void vhost_vsock_clear_iotlb(struct vhost_vsock *vsock, u64 features)
+{
+	struct vhost_iotlb *iotlb;
+	struct vhost_virtqueue *vq;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++)
+		mutex_lock_nested(&vsock->vqs[i].mutex, i);
+
+	iotlb = vsock->dev.iotlb;
+	vsock->dev.iotlb = NULL;
+
+	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
+		vq = &vsock->vqs[i];
+		vq->iotlb = NULL;
+		memset(vq->meta_iotlb, 0, sizeof(vq->meta_iotlb));
+		vq->acked_features = features;
+	}
+
+	for (i = ARRAY_SIZE(vsock->vqs); i-- > 0;)
+		mutex_unlock(&vsock->vqs[i].mutex);
+
+	vhost_clear_msg(&vsock->dev);
+	vhost_iotlb_free(iotlb);
+	wake_up_interruptible_poll(&vsock->dev.wait, EPOLLIN | EPOLLRDNORM);
+}
+
 static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 {
 	struct vhost_virtqueue *vq;
@@ -872,11 +900,16 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 
 	vsock->seqpacket_allow = features & (1ULL << VIRTIO_VSOCK_F_SEQPACKET);
 
-	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
-		vq = &vsock->vqs[i];
-		mutex_lock(&vq->mutex);
-		vq->acked_features = features;
-		mutex_unlock(&vq->mutex);
+	if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)) &&
+	    vsock->dev.iotlb) {
+		vhost_vsock_clear_iotlb(vsock, features);
+	} else {
+		for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
+			vq = &vsock->vqs[i];
+			mutex_lock(&vq->mutex);
+			vq->acked_features = features;
+			mutex_unlock(&vq->mutex);
+		}
 	}
 	mutex_unlock(&vsock->dev.mutex);
 	return 0;
-- 
2.34.1