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-rw-r--r--drivers/vhost/Kconfig15
-rw-r--r--drivers/vhost/vhost.c85
-rw-r--r--drivers/vhost/vhost.h11
-rw-r--r--include/uapi/linux/vhost.h14
4 files changed, 122 insertions, 3 deletions
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 017a1e8a8f6f..533eaf04f12f 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -32,3 +32,18 @@ config VHOST
---help---
This option is selected by any driver which needs to access
the core of vhost.
+
+config VHOST_CROSS_ENDIAN_LEGACY
+ bool "Cross-endian support for vhost"
+ default n
+ ---help---
+ This option allows vhost to support guests with a different byte
+ ordering from host while using legacy virtio.
+
+ Userspace programs can control the feature using the
+ VHOST_SET_VRING_ENDIAN and VHOST_GET_VRING_ENDIAN ioctls.
+
+ This is only useful on a few platforms (ppc64 and arm64). Since it
+ adds some overhead, it is disabled by default.
+
+ If unsure, say "N".
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2ee28266fd07..9e8e004bb1c3 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -36,6 +36,77 @@ enum {
#define vhost_used_event(vq) ((__virtio16 __user *)&vq->avail->ring[vq->num])
#define vhost_avail_event(vq) ((__virtio16 __user *)&vq->used->ring[vq->num])
+#ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY
+static void vhost_vq_reset_user_be(struct vhost_virtqueue *vq)
+{
+ vq->user_be = !virtio_legacy_is_little_endian();
+}
+
+static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp)
+{
+ struct vhost_vring_state s;
+
+ if (vq->private_data)
+ return -EBUSY;
+
+ if (copy_from_user(&s, argp, sizeof(s)))
+ return -EFAULT;
+
+ if (s.num != VHOST_VRING_LITTLE_ENDIAN &&
+ s.num != VHOST_VRING_BIG_ENDIAN)
+ return -EINVAL;
+
+ vq->user_be = s.num;
+
+ return 0;
+}
+
+static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx,
+ int __user *argp)
+{
+ struct vhost_vring_state s = {
+ .index = idx,
+ .num = vq->user_be
+ };
+
+ if (copy_to_user(argp, &s, sizeof(s)))
+ return -EFAULT;
+
+ return 0;
+}
+
+static void vhost_init_is_le(struct vhost_virtqueue *vq)
+{
+ /* Note for legacy virtio: user_be is initialized at reset time
+ * according to the host endianness. If userspace does not set an
+ * explicit endianness, the default behavior is native endian, as
+ * expected by legacy virtio.
+ */
+ vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq->user_be;
+}
+#else
+static void vhost_vq_reset_user_be(struct vhost_virtqueue *vq)
+{
+}
+
+static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp)
+{
+ return -ENOIOCTLCMD;
+}
+
+static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx,
+ int __user *argp)
+{
+ return -ENOIOCTLCMD;
+}
+
+static void vhost_init_is_le(struct vhost_virtqueue *vq)
+{
+ if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
+ vq->is_le = true;
+}
+#endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */
+
static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
poll_table *pt)
{
@@ -199,6 +270,8 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->call = NULL;
vq->log_ctx = NULL;
vq->memory = NULL;
+ vq->is_le = virtio_legacy_is_little_endian();
+ vhost_vq_reset_user_be(vq);
}
static int vhost_worker(void *data)
@@ -806,6 +879,12 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
} else
filep = eventfp;
break;
+ case VHOST_SET_VRING_ENDIAN:
+ r = vhost_set_vring_endian(vq, argp);
+ break;
+ case VHOST_GET_VRING_ENDIAN:
+ r = vhost_get_vring_endian(vq, idx, argp);
+ break;
default:
r = -ENOIOCTLCMD;
}
@@ -1044,8 +1123,12 @@ int vhost_init_used(struct vhost_virtqueue *vq)
{
__virtio16 last_used_idx;
int r;
- if (!vq->private_data)
+ if (!vq->private_data) {
+ vq->is_le = virtio_legacy_is_little_endian();
return 0;
+ }
+
+ vhost_init_is_le(vq);
r = vhost_update_used_flags(vq);
if (r)
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index a4fa33a79bf2..ce6f6da4b09f 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -106,6 +106,14 @@ struct vhost_virtqueue {
/* Log write descriptors */
void __user *log_base;
struct vhost_log *log;
+
+ /* Ring endianness. Defaults to legacy native endianness.
+ * Set to true when starting a modern virtio device. */
+ bool is_le;
+#ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY
+ /* Ring endianness requested by userspace for cross-endian support. */
+ bool user_be;
+#endif
};
struct vhost_dev {
@@ -175,8 +183,7 @@ static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit)
static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)
{
- return vhost_has_feature(vq, VIRTIO_F_VERSION_1) ||
- virtio_legacy_is_little_endian();
+ return vq->is_le;
}
/* Memory accessors */
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index bb6a5b4cb3c5..ab3731917bac 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -103,6 +103,20 @@ struct vhost_memory {
/* Get accessor: reads index, writes value in num */
#define VHOST_GET_VRING_BASE _IOWR(VHOST_VIRTIO, 0x12, struct vhost_vring_state)
+/* Set the vring byte order in num. Valid values are VHOST_VRING_LITTLE_ENDIAN
+ * or VHOST_VRING_BIG_ENDIAN (other values return -EINVAL).
+ * The byte order cannot be changed while the device is active: trying to do so
+ * returns -EBUSY.
+ * This is a legacy only API that is simply ignored when VIRTIO_F_VERSION_1 is
+ * set.
+ * Not all kernel configurations support this ioctl, but all configurations that
+ * support SET also support GET.
+ */
+#define VHOST_VRING_LITTLE_ENDIAN 0
+#define VHOST_VRING_BIG_ENDIAN 1
+#define VHOST_SET_VRING_ENDIAN _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_state)
+#define VHOST_GET_VRING_ENDIAN _IOW(VHOST_VIRTIO, 0x14, struct vhost_vring_state)
+
/* The following ioctls use eventfd file descriptors to signal and poll
* for events. */