diff options
| -rw-r--r-- | hw/virtio/virtio.c | 26 |
1 files changed, 22 insertions, 4 deletions
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 82e64144cc..9608358c85 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -70,8 +70,13 @@ typedef struct VRing struct VirtQueue { VRing vring; + + /* Next head to pop */ uint16_t last_avail_idx; + /* Last avail_idx read from VQ. */ + uint16_t shadow_avail_idx; + uint16_t used_idx; /* Last used index value we have signalled on */ @@ -132,7 +137,8 @@ static inline uint16_t vring_avail_idx(VirtQueue *vq) { hwaddr pa; pa = vq->vring.avail + offsetof(VRingAvail, idx); - return virtio_lduw_phys(vq->vdev, pa); + vq->shadow_avail_idx = virtio_lduw_phys(vq->vdev, pa); + return vq->shadow_avail_idx; } static inline uint16_t vring_avail_ring(VirtQueue *vq, int i) @@ -223,8 +229,14 @@ int virtio_queue_ready(VirtQueue *vq) return vq->vring.avail != 0; } +/* Fetch avail_idx from VQ memory only when we really need to know if + * guest has added some buffers. */ int virtio_queue_empty(VirtQueue *vq) { + if (vq->shadow_avail_idx != vq->last_avail_idx) { + return 0; + } + return vring_avail_idx(vq) == vq->last_avail_idx; } @@ -300,7 +312,7 @@ static int virtqueue_num_heads(VirtQueue *vq, unsigned int idx) /* Check it isn't doing very strange things with descriptor numbers. */ if (num_heads > vq->vring.num) { error_report("Guest moved used index from %u to %u", - idx, vring_avail_idx(vq)); + idx, vq->shadow_avail_idx); exit(1); } /* On success, callers read a descriptor at vq->last_avail_idx. @@ -535,9 +547,12 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz) struct iovec iov[VIRTQUEUE_MAX_SIZE]; VRingDesc desc; - if (!virtqueue_num_heads(vq, vq->last_avail_idx)) { + if (virtio_queue_empty(vq)) { return NULL; } + /* Needed after virtio_queue_empty(), see comment in + * virtqueue_num_heads(). */ + smp_rmb(); /* When we start there are none of either input nor output. */ out_num = in_num = 0; @@ -786,6 +801,7 @@ void virtio_reset(void *opaque) vdev->vq[i].vring.avail = 0; vdev->vq[i].vring.used = 0; vdev->vq[i].last_avail_idx = 0; + vdev->vq[i].shadow_avail_idx = 0; vdev->vq[i].used_idx = 0; virtio_queue_set_vector(vdev, i, VIRTIO_NO_VECTOR); vdev->vq[i].signalled_used = 0; @@ -1155,7 +1171,7 @@ static bool vring_notify(VirtIODevice *vdev, VirtQueue *vq) smp_mb(); /* Always notify when queue is empty (when feature acknowledge) */ if (virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFY_ON_EMPTY) && - !vq->inuse && vring_avail_idx(vq) == vq->last_avail_idx) { + !vq->inuse && virtio_queue_empty(vq)) { return true; } @@ -1579,6 +1595,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id) return -1; } vdev->vq[i].used_idx = vring_used_idx(&vdev->vq[i]); + vdev->vq[i].shadow_avail_idx = vring_avail_idx(&vdev->vq[i]); } } @@ -1714,6 +1731,7 @@ 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) { vdev->vq[n].last_avail_idx = idx; + vdev->vq[n].shadow_avail_idx = idx; } void virtio_queue_invalidate_signalled_used(VirtIODevice *vdev, int n) |