From: Greg Kurz <gkurz@linux.vnet.ibm.com>
Date: Fri, 20 Feb 2015 11:32:59 +0100
Message-ID: <20150220103259.22408.58874.stgit@bahia.local>
In-Reply-To: <20150220103253.22408.6807.stgit@bahia.local>
References: <20150220103253.22408.6807.stgit@bahia.local>
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Subject: [Qemu-devel] [PATCH 1/2] vhost: add VHOST_VRING_F_LEGACY_BIG_ENDIAN
	flag
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>, qemu-devel@nongnu.org

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;