On 11/09/2015 07:04 PM, Michael S. Tsirkin wrote:
On Fri, Oct 30, 2015 at 01:56:13PM +0800, Xiao Guangrong wrote:
QEMU keeps the state of memory of dimm device during live migration,
however, it is not enough for nvdimm device as its memory does not
contain its label data, so that we should protect the whole backend
memory instead

Signed-off-by: Xiao Guangrong <guangrong.x...@linux.intel.com>

It looks like there's now a difference between
host_memory_backend_get_memory and get_memory_region,
whereas previously they were exactly interchangeable.

Yes, it is. host_memory_backend_get_memory() is used to get the whole
backend memory region. get_memory_region() is used to get the memory region
which will be mapped to guest's address space. They are on the same page
for pc-dimm, but it's different for nvdimm since part of backend memory used
as label data which is not directly mapped to guest.

This needs some thought, in particular the theoretically
generic dimm.c has to do tricks to accomodate nvdimm.

The missing piece for NVDIMM is the 128k label space at the end,
right?  Can't nvdimm specific code just register that as a
separate RAM chunk in order to migrate it?

Yes, it is.

I thought this before, then we need to have addition callbackes:
- plug(), which is called when the dimm device is plugged, then nvdimm
  has the chance to do it own migration things.

- unplug(), let nvdimm undo the thing of migration.

It needs more codes but the logic seems more clear. If you like this way,
i will do.

  hw/mem/dimm.c | 14 ++++++++++++--
  1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/hw/mem/dimm.c b/hw/mem/dimm.c
index 498d380..44447d1 100644
--- a/hw/mem/dimm.c
+++ b/hw/mem/dimm.c
@@ -134,9 +134,16 @@ void dimm_memory_plug(DeviceState *dev, MemoryHotplugState 

      memory_region_add_subregion(&hpms->mr, addr - hpms->base, mr);
-    vmstate_register_ram(mr, dev);
      numa_set_mem_node_id(addr, memory_region_size(mr), dimm->node);

+    /*
+     * save the state only for @mr is not enough as it does not contain
+     * the label data of NVDIMM device, so that we keep the state of
+     * whole hostmem instead.
+     */
+    vmstate_register_ram(host_memory_backend_get_memory(dimm->hostmem, errp),
+                         dev);
      error_propagate(errp, local_err);
@@ -145,10 +152,13 @@ void dimm_memory_unplug(DeviceState *dev, 
MemoryHotplugState *hpms,
                             MemoryRegion *mr)
      DIMMDevice *dimm = DIMM(dev);
+    MemoryRegion *backend_mr;
+    backend_mr = host_memory_backend_get_memory(dimm->hostmem, &error_abort);

      numa_unset_mem_node_id(dimm->addr, memory_region_size(mr), dimm->node);
      memory_region_del_subregion(&hpms->mr, mr);
-    vmstate_unregister_ram(mr, dev);
+    vmstate_unregister_ram(backend_mr, dev);

  int qmp_dimm_device_list(Object *obj, void *opaque)

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