vhost: switch to use new message format

We use to have message like:

struct vhost_msg {
	int type;
	union {
		struct vhost_iotlb_msg iotlb;
		__u8 padding[64];
	};
};

Unfortunately, there will be a hole of 32bit in 64bit machine because
of the alignment. This leads a different formats between 32bit API and
64bit API. What's more it will break 32bit program running on 64bit
machine.

So fixing this by introducing a new message type with an explicit
32bit reserved field after type like:

struct vhost_msg_v2 {
	__u32 type;
	__u32 reserved;
	union {
		struct vhost_iotlb_msg iotlb;
		__u8 padding[64];
	};
};

We will have a consistent ABI after switching to use this. To enable
this capability, introduce a new ioctl (VHOST_SET_BAKCEND_FEATURE) for
userspace to enable this feature (VHOST_BACKEND_F_IOTLB_V2).

Fixes: 6b1e6cc7855b ("vhost: new device IOTLB API")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 30 insertions, 0 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 367d8023b54d..4e656f89cb22 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -78,6 +78,10 @@ enum {
 };
 
 enum {
+	VHOST_NET_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
+};
+
+enum {
 	VHOST_NET_VQ_RX = 0,
 	VHOST_NET_VQ_TX = 1,
 	VHOST_NET_VQ_MAX = 2,
@@ -1399,6 +1403,21 @@ done:
 	return err;
 }
 
+static int vhost_net_set_backend_features(struct vhost_net *n, u64 features)
+{
+	int i;
+
+	mutex_lock(&n->dev.mutex);
+	for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
+		mutex_lock(&n->vqs[i].vq.mutex);
+		n->vqs[i].vq.acked_backend_features = features;
+		mutex_unlock(&n->vqs[i].vq.mutex);
+	}
+	mutex_unlock(&n->dev.mutex);
+
+	return 0;
+}
+
 static int vhost_net_set_features(struct vhost_net *n, u64 features)
 {
 	size_t vhost_hlen, sock_hlen, hdr_len;
@@ -1489,6 +1508,17 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
 		if (features & ~VHOST_NET_FEATURES)
 			return -EOPNOTSUPP;
 		return vhost_net_set_features(n, features);
+	case VHOST_GET_BACKEND_FEATURES:
+		features = VHOST_NET_BACKEND_FEATURES;
+		if (copy_to_user(featurep, &features, sizeof(features)))
+			return -EFAULT;
+		return 0;
+	case VHOST_SET_BACKEND_FEATURES:
+		if (copy_from_user(&features, featurep, sizeof(features)))
+			return -EFAULT;
+		if (features & ~VHOST_NET_BACKEND_FEATURES)
+			return -EOPNOTSUPP;
+		return vhost_net_set_backend_features(n, features);
 	case VHOST_RESET_OWNER:
 		return vhost_net_reset_owner(n);
 	case VHOST_SET_OWNER: