[Qemu-devel] [PATCH] virtio-balloon: Fix ballooning not working correctly when hotplug memory

[zhanghailiang]

When do memory balloon, it references the ram_size as the real ram size of VM,
But here ram_size is not include the hotplugged memory, and the result will
be confused.

Steps to reproduce:
(1)Start VM: qemu -m size=1024,slots=4,maxmem=8G
(2)In VM: #free -m : 1024M
(3)qmp balloon 512M
(4)In VM: #free -m : 512M
(5)hotplug pc-dimm 1G
(6)In VM: #free -m : 1512M
(7)qmp balloon 256M
(8)In VM: #free -m :1256M

Here we add a new global variable 'vm_ram_size', it will stat
the VM's real ram size which include configured ram and hotplugged ram.
virtio-balloon will reference this parameter.

Signed-off-by: zhanghailiang <address@hidden>
---
 hw/i386/pc.c               |  1 +
 hw/virtio/virtio-balloon.c | 10 +++++-----
 include/exec/cpu-common.h  |  1 +
 vl.c                       |  3 +++
 4 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index b6c9b61..817810b 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1606,6 +1606,7 @@ static void pc_dimm_plug(HotplugHandler *hotplug_dev,
     memory_region_add_subregion(&pcms->hotplug_memory,
                                 addr - pcms->hotplug_memory_base, mr);
     vmstate_register_ram(mr, dev);
+    vm_ram_size += memory_region_size(mr);
 
     hhc = HOTPLUG_HANDLER_GET_CLASS(pcms->acpi_dev);
     hhc->plug(HOTPLUG_HANDLER(pcms->acpi_dev), dev, &local_err);
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 2c30b3d..205e1fe 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -292,7 +292,7 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
     memcpy(&config, config_data, sizeof(struct virtio_balloon_config));
     dev->actual = le32_to_cpu(config.actual);
     if (dev->actual != oldactual) {
-        qapi_event_send_balloon_change(ram_size -
+        qapi_event_send_balloon_change(vm_ram_size -
                         ((ram_addr_t) dev->actual << VIRTIO_BALLOON_PFN_SHIFT),
                         &error_abort);
     }
@@ -307,7 +307,7 @@ static uint32_t virtio_balloon_get_features(VirtIODevice 
*vdev, uint32_t f)
 static void virtio_balloon_stat(void *opaque, BalloonInfo *info)
 {
     VirtIOBalloon *dev = opaque;
-    info->actual = ram_size - ((uint64_t) dev->actual <<
+    info->actual = vm_ram_size - ((uint64_t) dev->actual <<
                                VIRTIO_BALLOON_PFN_SHIFT);
 }
 
@@ -316,11 +316,11 @@ static void virtio_balloon_to_target(void *opaque, 
ram_addr_t target)
     VirtIOBalloon *dev = VIRTIO_BALLOON(opaque);
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
 
-    if (target > ram_size) {
-        target = ram_size;
+    if (target > vm_ram_size) {
+        target = vm_ram_size;
     }
     if (target) {
-        dev->num_pages = (ram_size - target) >> VIRTIO_BALLOON_PFN_SHIFT;
+        dev->num_pages = (vm_ram_size - target) >> VIRTIO_BALLOON_PFN_SHIFT;
         virtio_notify_config(vdev);
     }
 }
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index e3ec4c8..f55db6a 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -46,6 +46,7 @@ typedef uintptr_t ram_addr_t;
 #endif
 
 extern ram_addr_t ram_size;
+extern ram_addr_t vm_ram_size;
 
 /* memory API */
 
diff --git a/vl.c b/vl.c
index 9c9acf5..5d20d0c 100644
--- a/vl.c
+++ b/vl.c
@@ -132,6 +132,7 @@ DisplayType display_type = DT_DEFAULT;
 static int display_remote;
 const char* keyboard_layout = NULL;
 ram_addr_t ram_size;
+ram_addr_t vm_ram_size; /* ram_size + hotplugged ram size */
 const char *mem_path = NULL;
 int mem_prealloc = 0; /* force preallocation of physical target memory */
 int nb_nics;
@@ -3015,6 +3016,7 @@ int main(int argc, char **argv, char **envp)
     machine_class = find_default_machine();
     cpu_model = NULL;
     ram_size = default_ram_size;
+    vm_ram_size = ram_size;
     snapshot = 0;
     cyls = heads = secs = 0;
     translation = BIOS_ATA_TRANSLATION_AUTO;
@@ -3388,6 +3390,7 @@ int main(int argc, char **argv, char **envp)
                             "'%s' option\n", slots_str ? "maxmem" : "slots");
                     exit(EXIT_FAILURE);
                 }
+                vm_ram_size = ram_size;
                 break;
             }
 #ifdef CONFIG_TPM
-- 
1.7.12.4