Re: [RFC PATCH 1/3] hw/intc/s390_flic: Migrate pending state

[David Hildenbrand <david@redhat.com>]

Am 26.05.24 um 21:44 schrieb Richard Henderson:
> On 5/26/24 08:53, David Hildenbrand wrote:
>> Am 25.05.24 um 15:12 schrieb Nicholas Piggin:
>>> The flic pending state is not migrated, so if the machine is migrated
>>> while an interrupt is pending, it can be lost. This shows up in
>>> qtest migration test, an extint is pending (due to console writes?)
>>> and the CPU waits via s390_cpu_set_psw and expects the interrupt to
>>> wake it. However when the flic pending state is lost, s390_cpu_has_int
>>> returns false, so s390_cpu_exec_interrupt falls through to halting
>>> again.
>>>
>>> Fix this by migrating pending. This prevents the qtest from hanging.
>>> Does service_param need to be migrated? Or the IO lists?
>>>
>>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>>> ---
>>>   hw/intc/s390_flic.c | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/hw/intc/s390_flic.c b/hw/intc/s390_flic.c
>>> index 6771645699..b70cf2295a 100644
>>> --- a/hw/intc/s390_flic.c
>>> +++ b/hw/intc/s390_flic.c
>>> @@ -369,6 +369,7 @@ static const VMStateDescription qemu_s390_flic_vmstate = {
>>>       .fields = (const VMStateField[]) {
>>>           VMSTATE_UINT8(simm, QEMUS390FLICState),
>>>           VMSTATE_UINT8(nimm, QEMUS390FLICState),
>>> +        VMSTATE_UINT32(pending, QEMUS390FLICState),
>>>           VMSTATE_END_OF_LIST()
>>>       }
>>>   };
>>
>> Likely you have to handle this using QEMU compat machines.
> 
> Well, since existing migration is broken, I don't think you have to preserve 

Migration is broken only in some case "while an interrupt is pending, it can be 
lost".

> compatibility.  But you do have to bump the version number.

Looking at it, this is TCG only, so likely we don't care that much about 
migration compatibility. But I have no idea what level of compatibility we want 
to support there.

-- 
Thanks,

David / dhildenb