From 257d8d98076717288519d312f1690c453bb74776 Mon Sep 17 00:00:00 2001
From: Maxime Coquelin <maxime.coquelin@redhat.com>
Date: Tue, 5 Dec 2017 09:28:38 +0100
Subject: [PATCH 16/21] virtio: Add queue interface to restore avail index from
 vring used index
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RH-Author: Maxime Coquelin <maxime.coquelin@redhat.com>
Message-id: <20171205092839.17597-2-maxime.coquelin@redhat.com>
Patchwork-id: 78140
O-Subject: [RHV7.5 qemu-kvm-rhev PATCH 1/2] virtio: Add queue interface to restore avail index from vring used index
Bugzilla: 1491909
RH-Acked-by: wexu@redhat.com
RH-Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
RH-Acked-by: Xiao Wang <jasowang@redhat.com>

In case of backend crash, it is not possible to restore internal
avail index from the backend value as vhost_get_vring_base
callback fails.

This patch provides a new interface to restore internal avail index
from the vring used index, as done by some vhost-user backend on
reconnection.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 2d4ba6cc741df15df6fbb4feaa706a02e103083a)
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/virtio/virtio.c         | 10 ++++++++++
 include/hw/virtio/virtio.h |  1 +
 2 files changed, 11 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index e7a2bc2..58ecf75 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2329,6 +2329,16 @@ void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx)
     vdev->vq[n].shadow_avail_idx = idx;
 }
 
+void virtio_queue_restore_last_avail_idx(VirtIODevice *vdev, int n)
+{
+    rcu_read_lock();
+    if (vdev->vq[n].vring.desc) {
+        vdev->vq[n].last_avail_idx = vring_used_idx(&vdev->vq[n]);
+        vdev->vq[n].shadow_avail_idx = vdev->vq[n].last_avail_idx;
+    }
+    rcu_read_unlock();
+}
+
 void virtio_queue_update_used_idx(VirtIODevice *vdev, int n)
 {
     rcu_read_lock();
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 5faa359..912310c 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -273,6 +273,7 @@ hwaddr virtio_queue_get_avail_size(VirtIODevice *vdev, int n);
 hwaddr virtio_queue_get_used_size(VirtIODevice *vdev, int n);
 uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n);
 void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx);
+void virtio_queue_restore_last_avail_idx(VirtIODevice *vdev, int n);
 void virtio_queue_invalidate_signalled_used(VirtIODevice *vdev, int n);
 void virtio_queue_update_used_idx(VirtIODevice *vdev, int n);
 VirtQueue *virtio_get_queue(VirtIODevice *vdev, int n);
-- 
1.8.3.1