diff options
| -rw-r--r-- | drivers/virtio/virtio_ring.c | 26 |
1 files changed, 22 insertions, 4 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 1ee97d402a4..827f7e04261 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -21,6 +21,24 @@ #include <linux/virtio_config.h> #include <linux/device.h> +/* virtio guest is communicating with a virtual "device" that actually runs on + * a host processor. Memory barriers are used to control SMP effects. */ +#ifdef CONFIG_SMP +/* Where possible, use SMP barriers which are more lightweight than mandatory + * barriers, because mandatory barriers control MMIO effects on accesses + * through relaxed memory I/O windows (which virtio does not use). */ +#define virtio_mb() smp_mb() +#define virtio_rmb() smp_rmb() +#define virtio_wmb() smp_wmb() +#else +/* We must force memory ordering even if guest is UP since host could be + * running on another CPU, but SMP barriers are defined to barrier() in that + * configuration. So fall back to mandatory barriers instead. */ +#define virtio_mb() mb() +#define virtio_rmb() rmb() +#define virtio_wmb() wmb() +#endif + #ifdef DEBUG /* For development, we want to crash whenever the ring is screwed. */ #define BAD_RING(_vq, fmt, args...) \ @@ -220,13 +238,13 @@ static void vring_kick(struct virtqueue *_vq) START_USE(vq); /* Descriptors and available array need to be set before we expose the * new available array entries. */ - wmb(); + virtio_wmb(); vq->vring.avail->idx += vq->num_added; vq->num_added = 0; /* Need to update avail index before checking if we should notify */ - mb(); + virtio_mb(); if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY)) /* Prod other side to tell it about changes. */ @@ -285,7 +303,7 @@ static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len) } /* Only get used array entries after they have been exposed by host. */ - rmb(); + virtio_rmb(); i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id; *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len; @@ -323,7 +341,7 @@ static bool vring_enable_cb(struct virtqueue *_vq) /* We optimistically turn back on interrupts, then check if there was * more to do. */ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; - mb(); + virtio_mb(); if (unlikely(more_used(vq))) { END_USE(vq); return false; |