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, 53 insertions, 18 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index a502f1af4a21..6f6c42d5e4be 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -315,6 +315,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	vq->log_addr = -1ull;
 	vq->private_data = NULL;
 	vq->acked_features = 0;
+	vq->acked_backend_features = 0;
 	vq->log_base = NULL;
 	vq->error_ctx = NULL;
 	vq->kick = NULL;
@@ -1027,28 +1028,40 @@ static int vhost_process_iotlb_msg(struct vhost_dev *dev,
 ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
 			     struct iov_iter *from)
 {
-	struct vhost_msg_node node;
-	unsigned size = sizeof(struct vhost_msg);
-	size_t ret;
-	int err;
+	struct vhost_iotlb_msg msg;
+	size_t offset;
+	int type, ret;
 
-	if (iov_iter_count(from) < size)
-		return 0;
-	ret = copy_from_iter(&node.msg, size, from);
-	if (ret != size)
+	ret = copy_from_iter(&type, sizeof(type), from);
+	if (ret != sizeof(type))
 		goto done;
 
-	switch (node.msg.type) {
+	switch (type) {
 	case VHOST_IOTLB_MSG:
-		err = vhost_process_iotlb_msg(dev, &node.msg.iotlb);
-		if (err)
-			ret = err;
+		/* There maybe a hole after type for V1 message type,
+		 * so skip it here.
+		 */
+		offset = offsetof(struct vhost_msg, iotlb) - sizeof(int);
+		break;
+	case VHOST_IOTLB_MSG_V2:
+		offset = sizeof(__u32);
 		break;
 	default:
 		ret = -EINVAL;
-		break;
+		goto done;
+	}
+
+	iov_iter_advance(from, offset);
+	ret = copy_from_iter(&msg, sizeof(msg), from);
+	if (ret != sizeof(msg))
+		goto done;
+	if (vhost_process_iotlb_msg(dev, &msg)) {
+		ret = -EFAULT;
+		goto done;
 	}
 
+	ret = (type == VHOST_IOTLB_MSG) ? sizeof(struct vhost_msg) :
+	      sizeof(struct vhost_msg_v2);
 done:
 	return ret;
 }
@@ -1107,13 +1120,28 @@ ssize_t vhost_chr_read_iter(struct vhost_dev *dev, struct iov_iter *to,
 		finish_wait(&dev->wait, &wait);
 
 	if (node) {
-		ret = copy_to_iter(&node->msg, size, to);
+		struct vhost_iotlb_msg *msg;
+		void *start = &node->msg;
+
+		switch (node->msg.type) {
+		case VHOST_IOTLB_MSG:
+			size = sizeof(node->msg);
+			msg = &node->msg.iotlb;
+			break;
+		case VHOST_IOTLB_MSG_V2:
+			size = sizeof(node->msg_v2);
+			msg = &node->msg_v2.iotlb;
+			break;
+		default:
+			BUG();
+			break;
+		}
 
-		if (ret != size || node->msg.type != VHOST_IOTLB_MISS) {
+		ret = copy_to_iter(start, size, to);
+		if (ret != size || msg->type != VHOST_IOTLB_MISS) {
 			kfree(node);
 			return ret;
 		}
-
 		vhost_enqueue_msg(dev, &dev->pending_list, node);
 	}
 
@@ -1126,12 +1154,19 @@ static int vhost_iotlb_miss(struct vhost_virtqueue *vq, u64 iova, int access)
 	struct vhost_dev *dev = vq->dev;
 	struct vhost_msg_node *node;
 	struct vhost_iotlb_msg *msg;
+	bool v2 = vhost_backend_has_feature(vq, VHOST_BACKEND_F_IOTLB_MSG_V2);
 
-	node = vhost_new_msg(vq, VHOST_IOTLB_MISS);
+	node = vhost_new_msg(vq, v2 ? VHOST_IOTLB_MSG_V2 : VHOST_IOTLB_MSG);
 	if (!node)
 		return -ENOMEM;
 
-	msg = &node->msg.iotlb;
+	if (v2) {
+		node->msg_v2.type = VHOST_IOTLB_MSG_V2;
+		msg = &node->msg_v2.iotlb;
+	} else {
+		msg = &node->msg.iotlb;
+	}
+
 	msg->type = VHOST_IOTLB_MISS;
 	msg->iova = iova;
 	msg->perm = access;