Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

Pull virtio/vhost cross endian support from Michael Tsirkin:
 "I have just queued some more bugfix patches today but none fix
  regressions and none are related to these ones, so it looks like a
  good time for a merge for -rc1.

  The motivation for this is support for legacy BE guests on the new LE
  hosts.  There are two redeeming properties that made me merge this:

   - It's a trivial amount of code: since we wrap host/guest accesses
     anyway, almost all of it is well hidden from drivers.

   - Sane platforms would never set flags like VHOST_CROSS_ENDIAN_LEGACY,
     and when it's clear, there's zero overhead (as some point it was
     tested by compiling with and without the patches, got the same
     stripped binary).

  Maybe we could create a Kconfig symbol to enforce the second point:
  prevent people from enabling it eg on x86.  I will look into this"

* tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost:
  virtio-pci: alloc only resources actually used.
  macvtap/tun: cross-endian support for little-endian hosts
  vhost: cross-endian support for legacy devices
  virtio: add explicit big-endian support to memory accessors
  vhost: introduce vhost_is_little_endian() helper
  vringh: introduce vringh_is_little_endian() helper
  macvtap: introduce macvtap_is_little_endian() helper
  tun: add tun_is_little_endian() helper
  virtio: introduce virtio_is_little_endian() helper

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".

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)

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 {
@@ -173,34 +181,39 @@ static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit)
 	return vq->acked_features & (1ULL << bit);
 }
 
+static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)
+{
+	return vq->is_le;
+}
+
 /* Memory accessors */
 static inline u16 vhost16_to_cpu(struct vhost_virtqueue *vq, __virtio16 val)
 {
-	return __virtio16_to_cpu(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
+	return __virtio16_to_cpu(vhost_is_little_endian(vq), val);
 }
 
 static inline __virtio16 cpu_to_vhost16(struct vhost_virtqueue *vq, u16 val)
 {
-	return __cpu_to_virtio16(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
+	return __cpu_to_virtio16(vhost_is_little_endian(vq), val);
 }
 
 static inline u32 vhost32_to_cpu(struct vhost_virtqueue *vq, __virtio32 val)
 {
-	return __virtio32_to_cpu(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
+	return __virtio32_to_cpu(vhost_is_little_endian(vq), val);
 }
 
 static inline __virtio32 cpu_to_vhost32(struct vhost_virtqueue *vq, u32 val)
 {
-	return __cpu_to_virtio32(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
+	return __cpu_to_virtio32(vhost_is_little_endian(vq), val);
 }
 
 static inline u64 vhost64_to_cpu(struct vhost_virtqueue *vq, __virtio64 val)
 {
-	return __virtio64_to_cpu(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
+	return __virtio64_to_cpu(vhost_is_little_endian(vq), val);
 }
 
 static inline __virtio64 cpu_to_vhost64(struct vhost_virtqueue *vq, u64 val)
 {
-	return __cpu_to_virtio64(vhost_has_feature(vq, VIRTIO_F_VERSION_1), val);
+	return __cpu_to_virtio64(vhost_is_little_endian(vq), val);
 }
 #endif