1 files changed, 52 insertions, 7 deletions

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index fbd2ecde93e4..0db906b3c95d 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...)                             \
@@ -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;
@@ -334,6 +351,30 @@ static bool vring_enable_cb(struct virtqueue *_vq)
         return true;
 }
 
+static void *vring_detach_unused_buf(struct virtqueue *_vq)
+{
+        struct vring_virtqueue *vq = to_vvq(_vq);
+        unsigned int i;
+        void *buf;
+
+        START_USE(vq);
+
+        for (i = 0; i < vq->vring.num; i++) {
+                if (!vq->data[i])
+                        continue;
+                /* detach_buf clears data, so grab it now. */
+                buf = vq->data[i];
+                detach_buf(vq, i);
+                END_USE(vq);
+                return buf;
+        }
+        /* That should have freed everything. */
+        BUG_ON(vq->num_free != vq->vring.num);
+
+        END_USE(vq);
+        return NULL;
+}
+
 irqreturn_t vring_interrupt(int irq, void *_vq)
 {
         struct vring_virtqueue *vq = to_vvq(_vq);
@@ -360,6 +401,7 @@ static struct virtqueue_ops vring_vq_ops = {
         .kick = vring_kick,
         .disable_cb = vring_disable_cb,
         .enable_cb = vring_enable_cb,
+        .detach_unused_buf = vring_detach_unused_buf,
 };
 
 struct virtqueue *vring_new_virtqueue(unsigned int num,
@@ -406,8 +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;
 }