qemu-kvm/kvm-vhost-Fix-device-s-used-descriptor-dequeue.patch

From 793d6d56190397624efdcaf6e0112bd12e39c05d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Eugenio=20P=C3=A9rez?= <eperezma@redhat.com>
Date: Thu, 21 Jul 2022 15:25:01 +0200
Subject: [PATCH 02/32] vhost: Fix device's used descriptor dequeue
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RH-Author: Eugenio Pérez <eperezma@redhat.com>
RH-MergeRequest: 108: Net Control Virtqueue shadow Support
RH-Commit: [2/27] b92803a0681c94c65d243dd07424522387594760 (eperezmartin/qemu-kvm)
RH-Bugzilla: 1939363
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
RH-Acked-by: Cindy Lu <lulu@redhat.com>
RH-Acked-by: Laurent Vivier <lvivier@redhat.com>

Bugzilla: https://bugzilla.redhat.com/1939363

Upstream Status: git://git.qemu.org/qemu.git

commit 81abfa5724c9a6502d7a1d3a67c55f2a303a1170
Author: Eugenio Pérez <eperezma@redhat.com>
Date:   Thu May 12 19:57:43 2022 +0200

    vhost: Fix device's used descriptor dequeue

    Only the first one of them were properly enqueued back.

    Fixes: 100890f7ca ("vhost: Shadow virtqueue buffers forwarding")

    Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
    Message-Id: <20220512175747.142058-3-eperezma@redhat.com>
    Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 3155801f50..31fc50907d 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -334,12 +334,22 @@ static void vhost_svq_disable_notification(VhostShadowVirtqueue *svq)
     svq->vring.avail->flags |= cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
 }
 
+static uint16_t vhost_svq_last_desc_of_chain(const VhostShadowVirtqueue *svq,
+                                             uint16_t num, uint16_t i)
+{
+    for (uint16_t j = 0; j < (num - 1); ++j) {
+        i = le16_to_cpu(svq->desc_next[i]);
+    }
+
+    return i;
+}
+
 static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
                                            uint32_t *len)
 {
     const vring_used_t *used = svq->vring.used;
     vring_used_elem_t used_elem;
-    uint16_t last_used;
+    uint16_t last_used, last_used_chain, num;
 
     if (!vhost_svq_more_used(svq)) {
         return NULL;
@@ -365,7 +375,10 @@ static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
         return NULL;
     }
 
-    svq->desc_next[used_elem.id] = svq->free_head;
+    num = svq->ring_id_maps[used_elem.id]->in_num +
+          svq->ring_id_maps[used_elem.id]->out_num;
+    last_used_chain = vhost_svq_last_desc_of_chain(svq, num, used_elem.id);
+    svq->desc_next[last_used_chain] = svq->free_head;
     svq->free_head = used_elem.id;
 
     *len = used_elem.len;
-- 
2.31.1