qemu-kvm/kvm-vhost-stop-transfer-elem-ownership-in-vhost_handle_g.patch

From 33c22dd3353f79a037f2473a69176932ac1a1c05 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Eugenio=20P=C3=A9rez?= <eperezma@redhat.com>
Date: Tue, 23 Aug 2022 20:30:26 +0200
Subject: [PATCH 08/29] vhost: stop transfer elem ownership in
 vhost_handle_guest_kick
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RH-Author: Laurent Vivier <lvivier@redhat.com>
RH-MergeRequest: 117: vDPA SVQ Multiqueue support
RH-Jira: RHELX-57
RH-Acked-by: Jason Wang <jasowang@redhat.com>
RH-Acked-by: Cindy Lu <lulu@redhat.com>
RH-Acked-by: Eugenio Pérez <eperezma@redhat.com>
RH-Commit: [8/25] e9c6314fddeb1f7bc738efea90f2788cae27bab7 (redhat/centos-stream/src/qemu-kvm)

It was easier to allow vhost_svq_add to handle the memory. Now that we
will allow qemu to add elements to a SVQ without the guest's knowledge,
it's better to handle it in the caller.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
(cherry picked from commit 9c2ab2f1ec333be8614cc12272d4b91960704dbe)
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 82a784d250..a1261d4a0f 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -233,9 +233,6 @@ static void vhost_svq_kick(VhostShadowVirtqueue *svq)
 /**
  * Add an element to a SVQ.
  *
- * The caller must check that there is enough slots for the new element. It
- * takes ownership of the element: In case of failure not ENOSPC, it is free.
- *
  * Return -EINVAL if element is invalid, -ENOSPC if dev queue is full
  */
 int vhost_svq_add(VhostShadowVirtqueue *svq, const struct iovec *out_sg,
@@ -252,7 +249,6 @@ int vhost_svq_add(VhostShadowVirtqueue *svq, const struct iovec *out_sg,
 
     ok = vhost_svq_add_split(svq, out_sg, out_num, in_sg, in_num, &qemu_head);
     if (unlikely(!ok)) {
-        g_free(elem);
         return -EINVAL;
     }
 
@@ -293,7 +289,7 @@ static void vhost_handle_guest_kick(VhostShadowVirtqueue *svq)
         virtio_queue_set_notification(svq->vq, false);
 
         while (true) {
-            VirtQueueElement *elem;
+            g_autofree VirtQueueElement *elem;
             int r;
 
             if (svq->next_guest_avail_elem) {
@@ -324,12 +320,14 @@ static void vhost_handle_guest_kick(VhostShadowVirtqueue *svq)
                      * queue the current guest descriptor and ignore kicks
                      * until some elements are used.
                      */
-                    svq->next_guest_avail_elem = elem;
+                    svq->next_guest_avail_elem = g_steal_pointer(&elem);
                 }
 
                 /* VQ is full or broken, just return and ignore kicks */
                 return;
             }
+            /* elem belongs to SVQ or external caller now */
+            elem = NULL;
         }
 
         virtio_queue_set_notification(svq->vq, true);
-- 
2.31.1