[Qemu-devel] [PATCH 0/2] vhost: support for cross endian

[Qemu-devel] [PATCH 0/2] vhost: support for cross endian

[Greg Kurz]

This patchset allows vhost_net to be used with legacy virtio when guest and
host have different endianness. It depends on the following kernel patchset:

https://lists.linuxfoundation.org/pipermail/virtualization/2015-February/029347.html

---

Cédric Le Goater (1):
      vhost_net: re-enable when cross endian

Greg Kurz (1):
      vhost: add VHOST_VRING_F_LEGACY_BIG_ENDIAN flag


 hw/net/vhost_net.c          |   19 -------------------
 hw/virtio/vhost.c           |   10 +++++++++-
 include/hw/virtio/vhost.h   |    1 +
 linux-headers/linux/vhost.h |    2 ++
 4 files changed, 12 insertions(+), 20 deletions(-)

--
Greg

[Qemu-devel] [PATCH 1/2] vhost: add VHOST_VRING_F_LEGACY_BIG_ENDIAN flag

[Greg Kurz]

When the guest and the host have a different endian order, the data
being accessed in the vring queues needs to be byteswapped if we run
in legacy mode.

This patch adds a flag to inform the vhost kernel backend about the
endianness to use.

This patch is based on previous work by Cédric Le Goater.

Cc: Cédric Le Goater <clg@fr.ibm.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
---
 hw/virtio/vhost.c           |   10 +++++++++-
 include/hw/virtio/vhost.h   |    1 +
 linux-headers/linux/vhost.h |    2 ++
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 5a12861..bd442f1 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -539,7 +539,13 @@ static int vhost_virtqueue_set_addr(struct vhost_dev *dev,
         .log_guest_addr = vq->used_phys,
         .flags = enable_log ? (1 << VHOST_VRING_F_LOG) : 0,
     };
-    int r = dev->vhost_ops->vhost_call(dev, VHOST_SET_VRING_ADDR, &addr);
+    int r;
+
+    if (vq->legacy_big_endian) {
+	addr.flags |= (1 << VHOST_VRING_F_LEGACY_BIG_ENDIAN);
+    }
+
+    r = dev->vhost_ops->vhost_call(dev, VHOST_SET_VRING_ADDR, &addr);
     if (r < 0) {
         return -errno;
     }
@@ -707,6 +713,8 @@ static int vhost_virtqueue_start(struct vhost_dev *dev,
         goto fail_alloc_ring;
     }
 
+    vq->legacy_big_endian = virtio_is_big_endian(vdev);
+
     r = vhost_virtqueue_set_addr(dev, vq, vhost_vq_index, dev->log_enabled);
     if (r < 0) {
         r = -errno;
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index d5593d1..991fa20 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -20,6 +20,7 @@ struct vhost_virtqueue {
     unsigned long long ring_phys;
     unsigned ring_size;
     EventNotifier masked_notifier;
+    bool legacy_big_endian; /* Only used with legacy virtio devices */
 };
 
 typedef unsigned long vhost_log_chunk_t;
diff --git a/linux-headers/linux/vhost.h b/linux-headers/linux/vhost.h
index c656f61..ffbb8ee 100644
--- a/linux-headers/linux/vhost.h
+++ b/linux-headers/linux/vhost.h
@@ -34,6 +34,8 @@ struct vhost_vring_addr {
 	/* Flag values: */
 	/* Whether log address is valid. If set enables logging. */
 #define VHOST_VRING_F_LOG 0
+	/* Whether we have a big-endian legacy virtio device. */
+#define VHOST_VRING_F_LEGACY_BIG_ENDIAN 1
 
 	/* Start of array of descriptors (virtually contiguous) */
 	__u64 desc_user_addr;

[Qemu-devel] [PATCH 2/2] vhost_net: re-enable when cross endian

[Greg Kurz]

From: Cédric Le Goater <clg@fr.ibm.com>

revert 371df9f5e0f1 "vhost-net: disable when cross-endian"

Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
---
 hw/net/vhost_net.c |   19 -------------------
 1 file changed, 19 deletions(-)

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index 4e3a061..721fb2d 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -271,19 +271,6 @@ static void vhost_net_stop_one(struct vhost_net *net,
     vhost_dev_disable_notifiers(&net->dev, dev);
 }
 
-static bool vhost_net_device_endian_ok(VirtIODevice *vdev)
-{
-#ifdef TARGET_IS_BIENDIAN
-#ifdef HOST_WORDS_BIGENDIAN
-    return virtio_is_big_endian(vdev);
-#else
-    return !virtio_is_big_endian(vdev);
-#endif
-#else
-    return true;
-#endif
-}
-
 int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
                     int total_queues)
 {
@@ -292,12 +279,6 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(vbus);
     int r, e, i;
 
-    if (!vhost_net_device_endian_ok(dev)) {
-        error_report("vhost-net does not support cross-endian");
-        r = -ENOSYS;
-        goto err;
-    }
-
     if (!k->set_guest_notifiers) {
         error_report("binding does not support guest notifiers");
         r = -ENOSYS;