[PATCH 0/2] vhost: Get vring base from vq, not svq

[PATCH 0/2] vhost: Get vring base from vq, not svq

[Eugenio Pérez]

The SVQ vring used idx usually match with the guest visible one, as long
as all the guest buffers (GPA) maps to exactly one buffer within qemu's
VA. However, as we can see in virtqueue_map_desc, a single guest buffer
could map to many buffers in SVQ vring.

The solution is to stop using the device's used idx and check for the
last avail idx. Since we cannot report in-flight descriptors with vdpa,
let's rewind all of them.

Also, move this rewind to the destination, so we keep migrating the in-flight
ones in case the destnation backend support them (vhost-kernel, emulated virtio
in qemu, etc.)

Eugenio Pérez (2):
  vhost: Get vring base from vq, not svq
  vhost: Move SVQ queue rewind to the destination

 hw/virtio/vhost-vdpa.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

-- 
2.31.1

[PATCH 1/2] vhost: Get vring base from vq, not svq

[Eugenio Pérez]

The SVQ vring used idx usually match with the guest visible one, as long
as all the guest buffers (GPA) maps to exactly one buffer within qemu's
VA. However, as we can see in virtqueue_map_desc, a single guest buffer
could map to many buffers in SVQ vring.

The solution is to stop using the device's used idx and check for the
last avail idx. Since we cannot report in-flight descriptors with vdpa,
let's rewind all of them.

Fixes: 6d0b22266633 ("vdpa: Adapt vhost_vdpa_get_vring_base to SVQ")
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-vdpa.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 795ed5a049..18820498b3 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -1194,11 +1194,10 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
                                        struct vhost_vring_state *ring)
 {
     struct vhost_vdpa *v = dev->opaque;
-    int vdpa_idx = ring->index - dev->vq_index;
     int ret;
 
     if (v->shadow_vqs_enabled) {
-        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, vdpa_idx);
+        VirtQueue *vq = virtio_get_queue(dev->vdev, ring->index);
 
         /*
          * Setting base as last used idx, so destination will see as available
@@ -1208,7 +1207,10 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
          * TODO: This is ok for networking, but other kinds of devices might
          * have problems with these retransmissions.
          */
-        ring->num = svq->last_used_idx;
+        while (virtqueue_rewind(vq, 1)) {
+            continue;
+        }
+        ring->num = virtio_queue_get_last_avail_idx(dev->vdev, ring->index);
         return 0;
     }
 
-- 
2.31.1

[PATCH 2/2] vhost: Move SVQ queue rewind to the destination

[Eugenio Pérez]

Migration with SVQ already migrate the inflight descriptors, so the
destination can perform the work.

This makes easier to migrate between backends or to recover them in
vhost devices that support set in flight descriptors.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-vdpa.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 18820498b3..4458c8d23e 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -1178,7 +1178,18 @@ static int vhost_vdpa_set_vring_base(struct vhost_dev *dev,
                                        struct vhost_vring_state *ring)
 {
     struct vhost_vdpa *v = dev->opaque;
+    VirtQueue *vq = virtio_get_queue(dev->vdev, ring->index);
 
+    /*
+     * vhost-vdpa devices does not support in-flight requests. Set all of them
+     * as available.
+     *
+     * TODO: This is ok for networking, but other kinds of devices might
+     * have problems with these retransmissions.
+     */
+    while (virtqueue_rewind(vq, 1)) {
+        continue;
+    }
     if (v->shadow_vqs_enabled) {
         /*
          * Device vring base was set at device start. SVQ base is handled by
@@ -1197,19 +1208,6 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
     int ret;
 
     if (v->shadow_vqs_enabled) {
-        VirtQueue *vq = virtio_get_queue(dev->vdev, ring->index);
-
-        /*
-         * Setting base as last used idx, so destination will see as available
-         * all the entries that the device did not use, including the in-flight
-         * processing ones.
-         *
-         * TODO: This is ok for networking, but other kinds of devices might
-         * have problems with these retransmissions.
-         */
-        while (virtqueue_rewind(vq, 1)) {
-            continue;
-        }
         ring->num = virtio_queue_get_last_avail_idx(dev->vdev, ring->index);
         return 0;
     }
-- 
2.31.1