Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/davej/cpufreq

[karo-tx-linux.git] / drivers / virtio / virtio_ring.c

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71929ee00d698b40f32d22b428e93b5f7dfcfbd4..0db906b3c95d71bd985fa97b2fc62c52a7244104 100644 (file)
--- 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...)                            \
@@ -36,10 +54,9 @@
                        panic("%s:in_use = %i\n",               \
                              (_vq)->vq.name, (_vq)->in_use);   \
                (_vq)->in_use = __LINE__;                       \
-               mb();                                           \
        } while (0)
 #define END_USE(_vq) \
-       do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; mb(); } while(0)
+       do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
 #else
 #define BAD_RING(_vq, fmt, args...)                            \
        do {                                                    \
@@ -221,13 +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. */
@@ -286,7 +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;
@@ -324,7 +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;
@@ -431,8 +448,11 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
        /* Put everything in free lists. */
        vq->num_free = num;
        vq->free_head = 0;
-       for (i = 0; i < num-1; i++)
+       for (i = 0; i < num-1; i++) {
                vq->vring.desc[i].next = i+1;
+               vq->data[i] = NULL;
+       }
+       vq->data[i] = NULL;
 
        return &vq->vq;
 }