diff options
Diffstat (limited to 'include/linux/virtio_ring.h')
| -rw-r--r-- | include/linux/virtio_ring.h | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index 63c6ea199519..ca3ad41c2c82 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -4,6 +4,63 @@ #include <linux/irqreturn.h> #include <uapi/linux/virtio_ring.h> +/* + * Barriers in virtio are tricky. Non-SMP virtio guests can't assume + * they're not on an SMP host system, so they need to assume real + * barriers. Non-SMP virtio hosts could skip the barriers, but does + * anyone care? + * + * For virtio_pci on SMP, we don't need to order with respect to MMIO + * accesses through relaxed memory I/O windows, so smp_mb() et al are + * sufficient. + * + * For using virtio to talk to real devices (eg. other heterogeneous + * CPUs) we do need real barriers. In theory, we could be using both + * kinds of virtio, so it's a runtime decision, and the branch is + * actually quite cheap. + */ + +#ifdef CONFIG_SMP +static inline void virtio_mb(bool weak_barriers) +{ + if (weak_barriers) + smp_mb(); + else + mb(); +} + +static inline void virtio_rmb(bool weak_barriers) +{ + if (weak_barriers) + smp_rmb(); + else + rmb(); +} + +static inline void virtio_wmb(bool weak_barriers) +{ + if (weak_barriers) + smp_wmb(); + else + wmb(); +} +#else +static inline void virtio_mb(bool weak_barriers) +{ + mb(); +} + +static inline void virtio_rmb(bool weak_barriers) +{ + rmb(); +} + +static inline void virtio_wmb(bool weak_barriers) +{ + wmb(); +} +#endif + struct virtio_device; struct virtqueue; |