From f221643835f73976adf07ebe355176b09decb558 Mon Sep 17 00:00:00 2001
From: Alex Williamson <alex.williamson@redhat.com>
Date: Mon, 11 Sep 2017 20:43:08 +0200
Subject: [PATCH 01/34] vhost: Release memory references on cleanup

RH-Author: Alex Williamson <alex.williamson@redhat.com>
Message-id: <20170911204254.12489.22036.stgit@redhat.home>
Patchwork-id: 76307
O-Subject: [RHEL-7.5 qemu-kvm-rhev PATCH 1/1] vhost: Release memory references on cleanup
Bugzilla: 1489670
RH-Acked-by: John Snow <jsnow@redhat.com>
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
RH-Acked-by: Auger Eric <eric.auger@redhat.com>

vhost registers a MemoryListener where it adds and removes references
to MemoryRegions as the MemoryRegionSections pass through.  The
region_add callback is invoked for each existing section when the
MemoryListener is registered, but unregistering the MemoryListener
performs no reciprocal region_del callback.  It's therefore the
owner of the MemoryListener's responsibility to cleanup any persistent
changes, such as these memory references, after unregistering.

The consequence of this bug is that if we have both a vhost device
and a vfio device, the vhost device will reference any mmap'd MMIO of
the vfio device via this MemoryListener.  If the vhost device is then
removed, those references remain outstanding.  If we then attempt to
remove the vfio device, it never gets finalized and the only way to
release the kernel file descriptors is to terminate the QEMU process.

Fixes: dfde4e6e1a86 ("memory: add ref/unref calls")
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-stable@nongnu.org # v1.6.0+
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit ee4c112846a0f2ac4fe5601918b0a2642ac8e2ed)
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/virtio/vhost.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 6eddb09..b737ca9 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1356,6 +1356,10 @@ void vhost_dev_cleanup(struct vhost_dev *hdev)
     if (hdev->mem) {
         /* those are only safe after successful init */
         memory_listener_unregister(&hdev->memory_listener);
+        for (i = 0; i < hdev->n_mem_sections; ++i) {
+            MemoryRegionSection *section = &hdev->mem_sections[i];
+            memory_region_unref(section->mr);
+        }
         QLIST_REMOVE(hdev, entry);
     }
     if (hdev->migration_blocker) {
-- 
1.8.3.1