[RFC v2 2/3] virtio: support delay of checks in virtio_load()

[Chuang Xu]

Delay checks in virtio_load() to avoid possible address_space_to_flatview() call
during memory region's begin/commit.

Signed-off-by: Chuang Xu <xuchuangxclwt@bytedance.com>
---
 hw/virtio/virtio.c      | 33 ++++++++++++++++++++++-----------
 include/sysemu/sysemu.h |  1 +
 softmmu/globals.c       |  3 +++
 3 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index eb6347ab5d..3e3fa2a89d 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -33,6 +33,7 @@
 #include "hw/virtio/virtio-access.h"
 #include "sysemu/dma.h"
 #include "sysemu/runstate.h"
+#include "sysemu/sysemu.h"
 #include "standard-headers/linux/virtio_ids.h"
 #include "standard-headers/linux/vhost_types.h"
 #include "standard-headers/linux/virtio_blk.h"
@@ -3642,8 +3643,20 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int 
version_id)
         vdev->start_on_kick = true;
     }
 
+    if (vdc->post_load) {
+        ret = vdc->post_load(vdev);
+        if (ret) {
+            return ret;
+        }
+    }
+
+    return 0;
+}
+
+static void virtio_load_check_delay(VirtIODevice *vdev)
+{
     RCU_READ_LOCK_GUARD();
-    for (i = 0; i < num; i++) {
+    for (int i = 0; i < VIRTIO_QUEUE_MAX; i++) {
         if (vdev->vq[i].vring.desc) {
             uint16_t nheads;
 
@@ -3696,19 +3709,12 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int 
version_id)
                              i, vdev->vq[i].vring.num,
                              vdev->vq[i].last_avail_idx,
                              vdev->vq[i].used_idx);
-                return -1;
+                abort();
             }
         }
     }
 
-    if (vdc->post_load) {
-        ret = vdc->post_load(vdev);
-        if (ret) {
-            return ret;
-        }
-    }
-
-    return 0;
+    return;
 }
 
 void virtio_cleanup(VirtIODevice *vdev)
@@ -4158,7 +4164,12 @@ static void virtio_memory_listener_commit(MemoryListener 
*listener)
         if (vdev->vq[i].vring.num == 0) {
             break;
         }
-        virtio_init_region_cache(vdev, i);
+
+        if (migration_enable_load_check_delay) {
+            virtio_load_check_delay(vdev);
+        } else {
+            virtio_init_region_cache(vdev, i);
+        }
     }
 }
 
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 6a7a31e64d..0523091445 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -12,6 +12,7 @@ extern int only_migratable;
 extern const char *qemu_name;
 extern QemuUUID qemu_uuid;
 extern bool qemu_uuid_set;
+extern bool migration_enable_load_check_delay;
 
 const char *qemu_get_vm_name(void);
 
diff --git a/softmmu/globals.c b/softmmu/globals.c
index 527edbefdd..1bd8f6c978 100644
--- a/softmmu/globals.c
+++ b/softmmu/globals.c
@@ -65,3 +65,6 @@ bool qemu_uuid_set;
 uint32_t xen_domid;
 enum xen_mode xen_mode = XEN_EMULATE;
 bool xen_domid_restrict;
+
+bool migration_enable_load_check_delay;
+
-- 
2.20.1