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, 10 insertions, 1 deletions

diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 6c844b90a168..466ef7542291 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -132,6 +132,7 @@ struct vhost_virtqueue {
 	struct vhost_umem *iotlb;
 	void *private_data;
 	u64 acked_features;
+	u64 acked_backend_features;
 	/* Log write descriptors */
 	void __user *log_base;
 	struct vhost_log *log;
@@ -147,7 +148,10 @@ struct vhost_virtqueue {
 };
 
 struct vhost_msg_node {
-  struct vhost_msg msg;
+  union {
+	  struct vhost_msg msg;
+	  struct vhost_msg_v2 msg_v2;
+  };
   struct vhost_virtqueue *vq;
   struct list_head node;
 };
@@ -238,6 +242,11 @@ static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit)
 	return vq->acked_features & (1ULL << bit);
 }
 
+static inline bool vhost_backend_has_feature(struct vhost_virtqueue *vq, int bit)
+{
+	return vq->acked_backend_features & (1ULL << bit);
+}
+
 #ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY
 static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)
 {