[PATCH] vhost/vsock: prevent stale IOTLB after ACCESS_PLATFORM changes

[Jia Jia <physicalmtea@gmail.com>]

vhost_vsock_set_features() initializes dev->iotlb when
VIRTIO_F_ACCESS_PLATFORM is enabled. It does not remove that IOTLB
when the feature is later cleared. The virtqueue still points at the
old IOTLB, and vhost_vsock_handle_tx_kick() passes descriptors to
vhost_get_vq_desc(), which translates them through that mapping.

A userspace backend can enable ACCESS_PLATFORM, install an IOTLB entry
for a payload GPA, start the device, clear ACCESS_PLATFORM, replace the
memory table, and reuse the old HVA before submitting the same GPA
again. The feature state then says direct memory access is in use
while the TX path still uses the old IOTLB HVA.

Reject clearing ACCESS_PLATFORM while the device IOTLB exists. Also
keep the existing IOTLB when a feature update leaves ACCESS_PLATFORM
enabled; VHOST_SET_FEATURES is used for runtime log updates and must
not discard the current translations by allocating an empty IOTLB.

Fixes: e13a6915a03f ("vhost/vsock: add IOTLB API support")
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/vhost/vsock.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index ae01457ea2cd..57e8fd1eb670 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -798,6 +798,7 @@ static int vhost_vsock_set_cid(struct vhost_vsock *vsock, u64 guest_cid)
 static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 {
 	struct vhost_virtqueue *vq;
+	int ret = -EFAULT;
 	int i;
 
 	if (features & ~VHOST_VSOCK_FEATURES)
@@ -809,7 +810,14 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 		goto err;
 	}
 
-	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
+	if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)) &&
+	    vsock->dev.iotlb) {
+		ret = -EBUSY;
+		goto err;
+	}
+
+	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)) &&
+	    !vsock->dev.iotlb) {
 		if (vhost_init_device_iotlb(&vsock->dev))
 			goto err;
 	}
@@ -827,7 +835,7 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 
 err:
 	mutex_unlock(&vsock->dev.mutex);
-	return -EFAULT;
+	return ret;
 }
 
 static long vhost_vsock_dev_ioctl(struct file *f, unsigned int ioctl,
-- 
2.34.1