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

[Peter Maydell]

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

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