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[PATCH-RFC,3/3] virtio: add missing barriers

Message ID 20091208161838.GD32188@redhat.com
State New
Headers show

Commit Message

Michael S. Tsirkin Dec. 8, 2009, 4:18 p.m. UTC 
Add missing memory barriers in virtio:
- before checking interrupt enabled bit, make sure
  data has been written to memory
- make sure ring index has been read before reading ring data

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/virtio.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)
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Patch

diff --git a/hw/virtio.c b/hw/virtio.c
index 9f020cf..bbd7b51 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -119,8 +119,12 @@  static inline uint16_t vring_avail_flags(VirtQueue *vq)
 static inline uint16_t vring_avail_idx(VirtQueue *vq)
 {
     target_phys_addr_t pa;
+    uint16_t idx;
     pa = vq->vring.avail + offsetof(VRingAvail, idx);
-    return lduw_phys(pa);
+    idx = lduw_phys(pa);
+    /* Make sure data read happens after index read */
+    rmb();
+    return idx;
 }
 
 static inline uint16_t vring_avail_ring(VirtQueue *vq, int i)
@@ -588,6 +592,8 @@  VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
 
 void virtio_notify(VirtIODevice *vdev, VirtQueue *vq)
 {
+    /* Make sure used ring is updated before we check NO_INTERRUPT. */
+    mb();
     /* Always notify when queue is empty (when feature acknowledge) */
     if ((vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT) &&
         (!(vdev->features & (1 << VIRTIO_F_NOTIFY_ON_EMPTY)) ||