[PATCH] virtio-pci: fix virtio_pci_queue_enabled()

[Laurent Vivier <lvivier@redhat.com>]

In legacy mode, virtio_pci_queue_enabled() falls back to
virtio_queue_enabled() to know if the queue is enabled.

But virtio_queue_enabled() calls again virtio_pci_queue_enabled()
if k->queue_enabled is set. This ends in a crash after a stack
overflow.

The problem can be reproduced with
"-device virtio-net-pci,disable-legacy=off,disable-modern=true
 -net tap,vhost=on"

And a look to the backtrace is very explicit:

    ...
    #4  0x000000010029a438 in virtio_queue_enabled ()
    #5  0x0000000100497a9c in virtio_pci_queue_enabled ()
    ...
    #130902 0x000000010029a460 in virtio_queue_enabled ()
    #130903 0x0000000100497a9c in virtio_pci_queue_enabled ()
    #130904 0x000000010029a460 in virtio_queue_enabled ()
    #130905 0x0000000100454a20 in vhost_net_start ()
    ...

This patch fixes the problem by introducing a new function
for the legacy case and calls it from virtio_pci_queue_enabled().
It also calls it from virtio_queue_enabled() to avoid code duplication.

Fixes: f19bcdfedd53 ("virtio-pci: implement queue_enabled method")
Cc: Jason Wang <jasowang@redhat.com>
Cc: Cindy Lu <lulu@redhat.com>
CC: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/virtio/virtio-pci.c     | 2 +-
 hw/virtio/virtio.c         | 7 ++++++-
 include/hw/virtio/virtio.h | 1 +
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index ada1101d07bf..4ad3ad81a2cf 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1116,7 +1116,7 @@ static bool virtio_pci_queue_enabled(DeviceState *d, int n)
         return proxy->vqs[vdev->queue_sel].enabled;
     }
 
-    return virtio_queue_enabled(vdev, n);
+    return virtio_queue_enabled_legacy(vdev, n);
 }
 
 static int virtio_pci_add_mem_cap(VirtIOPCIProxy *proxy,
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 546a198e79b0..e98302521769 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -3309,6 +3309,11 @@ hwaddr virtio_queue_get_desc_addr(VirtIODevice *vdev, int n)
     return vdev->vq[n].vring.desc;
 }
 
+bool virtio_queue_enabled_legacy(VirtIODevice *vdev, int n)
+{
+    return virtio_queue_get_desc_addr(vdev, n) != 0;
+}
+
 bool virtio_queue_enabled(VirtIODevice *vdev, int n)
 {
     BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
@@ -3317,7 +3322,7 @@ bool virtio_queue_enabled(VirtIODevice *vdev, int n)
     if (k->queue_enabled) {
         return k->queue_enabled(qbus->parent, n);
     }
-    return virtio_queue_get_desc_addr(vdev, n) != 0;
+    return virtio_queue_enabled_legacy(vdev, n);
 }
 
 hwaddr virtio_queue_get_avail_addr(VirtIODevice *vdev, int n)
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 198ffc762678..e424df12cf6d 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -295,6 +295,7 @@ typedef struct VirtIORNGConf VirtIORNGConf;
                       VIRTIO_F_RING_PACKED, false)
 
 hwaddr virtio_queue_get_desc_addr(VirtIODevice *vdev, int n);
+bool virtio_queue_enabled_legacy(VirtIODevice *vdev, int n);
 bool virtio_queue_enabled(VirtIODevice *vdev, int n);
 hwaddr virtio_queue_get_avail_addr(VirtIODevice *vdev, int n);
 hwaddr virtio_queue_get_used_addr(VirtIODevice *vdev, int n);
-- 
2.26.2