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Subject[PATCH net-next] vhost: switch to use new message format
Date
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 {
int 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>
---
drivers/vhost/net.c | 30 ++++++++++++++++++++
drivers/vhost/vhost.c | 71 ++++++++++++++++++++++++++++++++++------------
drivers/vhost/vhost.h | 11 ++++++-
include/uapi/linux/vhost.h | 18 ++++++++++++
4 files changed, 111 insertions(+), 19 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 367d802..4e656f8 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 @@ static long vhost_net_reset_owner(struct vhost_net *n)
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:
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index a502f1a..6f6c42d 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;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 6c844b9..466ef75 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)
{
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index c51f8e5..c176e9d 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -65,6 +65,7 @@ struct vhost_iotlb_msg {
};

#define VHOST_IOTLB_MSG 0x1
+#define VHOST_IOTLB_MSG_V2 0x2

struct vhost_msg {
int type;
@@ -74,6 +75,15 @@ struct vhost_msg {
};
};

+struct vhost_msg_v2 {
+ int type;
+ __u32 reserved;
+ union {
+ struct vhost_iotlb_msg iotlb;
+ __u8 padding[64];
+ };
+};
+
struct vhost_memory_region {
__u64 guest_phys_addr;
__u64 memory_size; /* bytes */
@@ -160,6 +170,14 @@ struct vhost_memory {
#define VHOST_GET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x24, \
struct vhost_vring_state)

+/* Set or get vhost backend capability */
+
+/* Use message type V2 */
+#define VHOST_BACKEND_F_IOTLB_MSG_V2 0x1
+
+#define VHOST_SET_BACKEND_FEATURES _IOW(VHOST_VIRTIO, 0x25, __u64)
+#define VHOST_GET_BACKEND_FEATURES _IOW(VHOST_VIRTIO, 0x26, __u64)
+
/* VHOST_NET specific defines */

/* Attach virtio net ring to a raw socket, or tap device.
--
2.7.4
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