Re: [PATCH v2] hw/isa/piix4: Migrate Reset Control Register

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

On 3/24/21 8:40 PM, Dr. David Alan Gilbert wrote:
> * Philippe Mathieu-Daudé (f4bug@amsat.org) wrote:
>> When adding the Reset register in commit 5790b757cfb we
>> forgot to migrate it.
>>
>> While it is possible a VM using the PIIX4 is migrated just
>> after requesting a system shutdown, it is very unlikely.
>> However when restoring a migrated VM, we might have the
>> RCR bit #4 set on the stack and when the VM resume it
>> directly shutdowns.
>>
>> Add a post_load() migration handler and set the default
>> RCR value to 0 for earlier versions, assuming the VM was
>> not going to shutdown before migration.
>>
>> Fixes: 5790b757cfb ("piix4: Add the Reset Control Register")
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>> v2: Add piix4_ide_post_load() and describe
>> ---
>>  hw/isa/piix4.c | 15 ++++++++++++++-
>>  1 file changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/isa/piix4.c b/hw/isa/piix4.c
>> index a50d97834c7..e7bce0e590c 100644
>> --- a/hw/isa/piix4.c
>> +++ b/hw/isa/piix4.c
>> @@ -93,12 +93,25 @@ static void piix4_isa_reset(DeviceState *dev)
>>      pci_conf[0xae] = 0x00;
>>  }
>>  
>> +static int piix4_ide_post_load(void *opaque, int version_id)
>> +{
>> +    PIIX4State *s = opaque;
>> +
>> +    if (version_id == 2) {
>> +        s->rcr = 0;
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>>  static const VMStateDescription vmstate_piix4 = {
>>      .name = "PIIX4",
>> -    .version_id = 2,
>> +    .version_id = 3,
>>      .minimum_version_id = 2,
>> +    .post_load = piix4_ide_post_load,
>>      .fields = (VMStateField[]) {
>>          VMSTATE_PCI_DEVICE(dev, PIIX4State),
>> +        VMSTATE_UINT8(rcr, PIIX4State),
> 
> I don't think that looks right any more; you'd need to make that a 
>    VMSTATE_UINT8_V(rcr, PIIX4State, 3),
> 
> I think, otherwise when you loaded a v2 it would still try
> and read the rcr byte.

Ah now I guess I understood.

Thanks!