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Subject[PATCHv2-RFC 2/2] virtio: publish used idx
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/net/virtio_net.c | 2 ++
drivers/virtio/virtio_ring.c | 17 +++++++++++++++--
include/linux/virtio_ring.h | 4 ++++
3 files changed, 21 insertions(+), 2 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 78eb319..30e7483 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -23,6 +23,7 @@
#include <linux/module.h>
#include <linux/virtio.h>
#include <linux/virtio_net.h>
+#include <linux/virtio_ring.h>
#include <linux/scatterlist.h>
#include <linux/if_vlan.h>
#include <linux/slab.h>
@@ -1056,6 +1057,7 @@ static unsigned int features[] = {
VIRTIO_NET_F_GUEST_ECN, VIRTIO_NET_F_GUEST_UFO,
VIRTIO_NET_F_MRG_RXBUF, VIRTIO_NET_F_STATUS, VIRTIO_NET_F_CTRL_VQ,
VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN,
+ VIRTIO_RING_F_PUBLISH_USED,
};

static struct virtio_driver virtio_net_driver = {
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 2241342..4a5458e 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -92,6 +92,9 @@ struct vring_virtqueue
/* Last used index we've seen. */
u16 last_used_idx;

+ /* Publish last used index we've seen at this location. */
+ u16 *publish_last_used_idx;
+
/* How to notify other side. FIXME: commonalize hcalls! */
void (*notify)(struct virtqueue *vq);

@@ -325,7 +328,7 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
/* detach_buf clears data, so grab it now. */
ret = vq->data[i];
detach_buf(vq, i);
- vq->last_used_idx++;
+ *vq->publish_last_used_idx = ++vq->last_used_idx;
END_USE(vq);
return ret;
}
@@ -348,6 +351,8 @@ bool virtqueue_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;
+ /* Besides flags write, this barrier also flushes out
+ * last available index write. */
virtio_mb();
if (unlikely(more_used(vq))) {
END_USE(vq);
@@ -425,13 +430,19 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
if (!vq)
return NULL;

- vring_init(&vq->vring, num, pages, vring_align, false);
+ vring_init(&vq->vring, num, pages, vring_align,
+ virtio_has_feature(vdev, VIRTIO_RING_F_PUBLISH_USED));
+ if (virtio_has_feature(vdev, VIRTIO_RING_F_PUBLISH_USED))
+ vq->publish_last_used_idx = &vq->vring.avail->last_used_idx;
+ else
+ vq->publish_last_used_idx = &vq->last_used_idx;
vq->vq.callback = callback;
vq->vq.vdev = vdev;
vq->vq.name = name;
vq->notify = notify;
vq->broken = false;
vq->last_used_idx = 0;
+ *vq->publish_last_used_idx = 0;
vq->num_added = 0;
list_add_tail(&vq->vq.list, &vdev->vqs);
#ifdef DEBUG
@@ -473,6 +484,8 @@ void vring_transport_features(struct virtio_device *vdev)
switch (i) {
case VIRTIO_RING_F_INDIRECT_DESC:
break;
+ case VIRTIO_RING_F_PUBLISH_USED:
+ break;
default:
/* We don't understand this bit. */
clear_bit(i, vdev->features);
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index c5f3ee7..0de35c5 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -29,6 +29,9 @@
/* We support indirect buffer descriptors */
#define VIRTIO_RING_F_INDIRECT_DESC 28

+/* The Guest publishes last-seen used index at the end of the avail ring. */
+#define VIRTIO_RING_F_PUBLISH_USED 29
+
/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
struct vring_desc {
/* Address (guest-physical). */
@@ -50,6 +53,7 @@ struct vring_avail {
struct vring_avail_ctrl {
__u16 flags;
__u16 idx;
+ __u16 last_used_idx;
};

/* u32 is used here for ids for padding reasons. */
--
1.7.1.12.g42b7f

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