Re: [Qemu-devel] [PATCH 0/3] Add new utility function memory_region_allocate_aux_memory()

[Igor Mammedov]

On Thu, 6 Jul 2017 15:52:44 +0100
Peter Maydell <address@hidden> wrote:

> On 5 July 2017 at 13:21, Paolo Bonzini <address@hidden> wrote:
> >
> >
> > On 04/07/2017 19:02, Peter Maydell wrote:  
> >> Many board models and several devices need to create auxiliary
> >> regions of RAM (in addition to the main lump of 'system' memory),
> >> to model static RAMs, video memory, ROMs, etc. Currently they do
> >> this with a sequence like:
> >>        memory_region_init_ram(sram, NULL, "sram", 0x10000, &error_fatal);
> >>        vmstate_register_ram_global(sram);  
> >
> > Instead of vmstate_register_ram_global, you should use
> >
> >     vmstate_register_ram(mr, owner);
> >
> > You should even do it for all memory regions, probably.  
> 
> This sounds like a good thing, but it's awkward for migration
> compatibility, because these callers to memory_region_init_ram()
> don't call vmstate_register_ram():
> 
> hw/arm/highbank.c (a bug)
> hw/mips/mips_malta.c (region is ro)
> hw/net/dp3893x.c (prom, ro, contains mac address)
> hw/pci-host/xilinx-pcie.c (dummy region; migrating wouldn't hurt)
> backends/hostmem-ram.c (bug, or is migration handled elsewhere?)
> 
> and if we add an implicit call then we break migration compat
> for those boards/devices.
> 
> > Only memory_region_init_ram_device_ptr (which sets mr->ram_device) must
> > not call vmstate_register_ram.  This is a bit ugly because it requires
> > inlining memory_region_init_ram_ptr into it.
> >
> > memory_region_init_ram_from_fd probably needs to be excluded, as well,
> > based on its sole user.  
> 
> Callers of memory_region_init_ram_from_file() which don't
> call vmstate_register_ram():
> backends/hostmem-ram.c

if backend is used by pc-dimm,
then it's pc-dimm job to (un)register vmstate:

pc_dimm_memory_plug()->vmstate_register_ram(vmstate_mr, dev);

> Callers of memory_region_init_ram_ptr() which don't call
> vmstate_register_ram():
> hw/misc/mmio_interface.c
>  -- seems to be an implementation detail of the exceute-from-device
>     support so maybe it doesn't need migration support ??
> 
> thanks
> -- PMM
>