On Fri, Aug 03, 2018 at 03:04:51PM +0800, Jason Wang wrote:
> 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
> ---
> 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(>dev.mutex);
> + for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
> + mutex_lock(>vqs[i].vq.mutex);
> + n->vqs[i].vq.acked_backend_features = features;
> + mutex_unlock(>vqs[i].vq.mutex);
> + }
> + mutex_unlock(>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, , sizeof(features)))
> + return -EFAULT;
> + return 0;
> + case VHOST_SET_BACKEND_FEATURES:
> + if (copy_from_user(, 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(, size, from);
> - if (ret != size)
> + ret = copy_from_iter(, 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, );
> - 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;
> +
