From 09047ffb4faaebd032d24f993e1e290c0369a7a3 Mon Sep 17 00:00:00 2001
From: Thomas Huth <thuth@redhat.com>
Date: Fri, 3 Jul 2015 19:13:35 +0200
Subject: [PATCH 025/100] vhost: set vring endianness for legacy virtio

Message-id: <1435950819-10991-4-git-send-email-thuth@redhat.com>
Patchwork-id: 66696
O-Subject: [RHEL7.2 qemu-kvm-rhev PATCH 3/7] vhost: set vring endianness for legacy virtio
Bugzilla: 1225715
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
RH-Acked-by: David Gibson <dgibson@redhat.com>

From: Greg Kurz <gkurz@linux.vnet.ibm.com>

Legacy virtio is native endian: if the guest and host endianness differ,
we have to tell vhost so it can swap bytes where appropriate. This is
done through a vhost ring ioctl.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 04b7a1523d65bb5c78832098cf3108a1aadcaf8a)
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/virtio/vhost.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 54851b7..1d7b939 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -17,9 +17,11 @@
 #include "hw/hw.h"
 #include "qemu/atomic.h"
 #include "qemu/range.h"
+#include "qemu/error-report.h"
 #include <linux/vhost.h>
 #include "exec/address-spaces.h"
 #include "hw/virtio/virtio-bus.h"
+#include "hw/virtio/virtio-access.h"
 #include "migration/migration.h"
 
 static void vhost_dev_sync_region(struct vhost_dev *dev,
@@ -647,6 +649,27 @@ static void vhost_log_stop(MemoryListener *listener,
     /* FIXME: implement */
 }
 
+static int vhost_virtqueue_set_vring_endian_legacy(struct vhost_dev *dev,
+                                                   bool is_big_endian,
+                                                   int vhost_vq_index)
+{
+    struct vhost_vring_state s = {
+        .index = vhost_vq_index,
+        .num = is_big_endian
+    };
+
+    if (!dev->vhost_ops->vhost_call(dev, VHOST_SET_VRING_ENDIAN, &s)) {
+        return 0;
+    }
+
+    if (errno == ENOTTY) {
+        error_report("vhost does not support cross-endian");
+        return -ENOSYS;
+    }
+
+    return -errno;
+}
+
 static int vhost_virtqueue_start(struct vhost_dev *dev,
                                 struct VirtIODevice *vdev,
                                 struct vhost_virtqueue *vq,
@@ -677,6 +700,16 @@ static int vhost_virtqueue_start(struct vhost_dev *dev,
         return -errno;
     }
 
+    if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1) &&
+        virtio_legacy_is_cross_endian(vdev)) {
+        r = vhost_virtqueue_set_vring_endian_legacy(dev,
+                                                    virtio_is_big_endian(vdev),
+                                                    vhost_vq_index);
+        if (r) {
+            return -errno;
+        }
+    }
+
     s = l = virtio_queue_get_desc_size(vdev, idx);
     a = virtio_queue_get_desc_addr(vdev, idx);
     vq->desc = cpu_physical_memory_map(a, &l, 0);
@@ -747,8 +780,9 @@ static void vhost_virtqueue_stop(struct vhost_dev *dev,
                                     struct vhost_virtqueue *vq,
                                     unsigned idx)
 {
+    int vhost_vq_index = idx - dev->vq_index;
     struct vhost_vring_state state = {
-        .index = idx - dev->vq_index
+        .index = vhost_vq_index,
     };
     int r;
     assert(idx >= dev->vq_index && idx < dev->vq_index + dev->nvqs);
@@ -759,6 +793,20 @@ static void vhost_virtqueue_stop(struct vhost_dev *dev,
     }
     virtio_queue_set_last_avail_idx(vdev, idx, state.num);
     virtio_queue_invalidate_signalled_used(vdev, idx);
+
+    /* In the cross-endian case, we need to reset the vring endianness to
+     * native as legacy devices expect so by default.
+     */
+    if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1) &&
+        virtio_legacy_is_cross_endian(vdev)) {
+        r = vhost_virtqueue_set_vring_endian_legacy(dev,
+                                                    !virtio_is_big_endian(vdev),
+                                                    vhost_vq_index);
+        if (r < 0) {
+            error_report("failed to reset vring endianness");
+        }
+    }
+
     assert (r >= 0);
     cpu_physical_memory_unmap(vq->ring, virtio_queue_get_ring_size(vdev, idx),
                               0, virtio_queue_get_ring_size(vdev, idx));
-- 
1.8.3.1