Re: [Qemu-devel] [PATCH v2 6/6] hw/arm/virt: Set minimum_page_bits to 12

[Peter Maydell]

On 21 June 2016 at 19:45, Andrew Jones <address@hidden> wrote:
> On Tue, Jun 21, 2016 at 06:09:34PM +0100, Peter Maydell wrote:
>> Since the virt board model will never create a CPU which is
>> pre-ARMv7, we know that our minimum page size is 4K and can
>> set minimum_page_bits accordingly, for improved performance.
>>
>> Note that this is a migration compatibility break.
>>
>> Signed-off-by: Peter Maydell <address@hidden>
>> ---
>>  hw/arm/virt.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index c5c125e..f9b51aa 100644
>> --- a/hw/arm/virt.c
>> +++ b/hw/arm/virt.c
>> @@ -1440,6 +1440,8 @@ static void virt_machine_class_init(ObjectClass *oc, 
>> void *data)
>>      mc->block_default_type = IF_VIRTIO;
>>      mc->no_cdrom = 1;
>>      mc->pci_allow_0_address = true;
>> +    /* We know we will never create a pre-ARMv7 CPU which needs 1K pages */
>> +    mc->minimum_page_bits = 12;
>>  }
>
> As this breaks migration, then I guess we also need
>
> @@ -1507,5 +1510,6 @@ static void virt_machine_2_6_options(MachineClass *mc)
>  {
>      virt_machine_2_7_options(mc);
>      SET_MACHINE_COMPAT(mc, VIRT_COMPAT_2_6);
> +    mc->minimum_page_bits = 10;
>  }
>  DEFINE_VIRT_MACHINE(2, 6)

Doesn't hurt, but are we trying to claim migration
compat between different QEMU versions with the
versioned-machine names ?

thanks
-- PMM