Re: [Qemu-devel] [PATCH v6 19/33] dimm: keep the state of the whole backend memory

[Michael S. Tsirkin]

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 <address@hidden>

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

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?

> ---
>  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 *hpms,
>      }
>  
>      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);
> +
>  out:
>      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)
> -- 
> 1.8.3.1