Re: [PATCH qemu v2 3/3] hw/s390x: support migration of CPI values

[shalini <shalini@imap.linux.ibm.com>]

On 2025-03-05 19:33, Thomas Huth wrote:
> On 24/02/2025 13.04, Shalini Chellathurai Saroja wrote:
>> Register Control-Program Identification data with the live
>> migration infrastructure.
>> 
>> Signed-off-by: Shalini Chellathurai Saroja <shalini@linux.ibm.com>
>> Reviewed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
>> ---
>>   hw/s390x/s390-virtio-ccw.c | 17 +++++++++++++++++
>>   1 file changed, 17 insertions(+)
>> 
>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
>> index 13ea8db1b0..4d0838d037 100644
>> --- a/hw/s390x/s390-virtio-ccw.c
>> +++ b/hw/s390x/s390-virtio-ccw.c
>> @@ -260,6 +260,20 @@ static void s390_create_sclpconsole(SCLPDevice 
>> *sclp,
>>       qdev_realize_and_unref(dev, ev_fac_bus, &error_fatal);
>>   }
>>   +static const VMStateDescription vmstate_control_program_id = {
>> +    .name = "s390_control_program_id",
>> +    .version_id = 0,
>> +    .minimum_version_id = 0,
>> +    .fields = (const VMStateField[]) {
>> +        VMSTATE_UINT8_ARRAY(system_type, ControlProgramId, 8),
>> +        VMSTATE_UINT8_ARRAY(system_name, ControlProgramId, 8),
>> +        VMSTATE_UINT64(system_level, ControlProgramId),
>> +        VMSTATE_UINT8_ARRAY(sysplex_name, ControlProgramId, 8),
>> +        VMSTATE_UINT64(timestamp, ControlProgramId),
>> +        VMSTATE_END_OF_LIST()
>> +    }
>> +};
>> +
>>   static void ccw_init(MachineState *machine)
>>   {
>>       MachineClass *mc = MACHINE_GET_CLASS(machine);
>> @@ -308,6 +322,9 @@ static void ccw_init(MachineState *machine)
>>       ret = css_create_css_image(VIRTUAL_CSSID, true);
>>       assert(ret == 0);
>>   +    /* register CPI values */
>> +    vmstate_register_any(NULL, &vmstate_control_program_id, 
>> &ms->cpi);
> 
>  Hi again,
> 
> after looking at this for a while, I think it might be cleaner to
> store the state in the TYPE_SCLP_CPI device instead of storing it in
> the machine state. Then you can also use dc->vmsd there instead of
> using the legacy vmstate_register_any() function.
> 

Hello Thomas,

The SCLP event type CPI is used to transfer the data mentioned below 
from guest operating system to QEMU. The job of the CPI event is 
complete, when this transfer is done.

The received data must be saved in the QEMU object model, so that it is 
possible for the user to retrieve the data via QMP. The received data 
provides information about the guest virtual machine.

System type - Operating system of the guest (eg: LINUX)
System name - Hostname provided to the guest (eg: TESTVM)
System level - Kernel version of the guest operating system (eg: 
0x50e00)
Sysplex name - Sysplex refers to a cluster of logical partitions  that 
communicates and co-operates with each other. Sysplex name is the name 
of the cluster which the guest belongs to(If any).(eg: PLEX)

In my perspective, I believe that the s390 machine state is appropriate 
for storing the data about the guest virtual machine. Please do let me 
know if you still want to change this?, thank you.

> Additionally, I think you need some compat handling for backward
> migration in your patches. E.g. have you tried migrating from an old
> version of QEMU to a newer one (that includes your patches) and then
> back to the old one?
> I think the TYPE_SCLP_CPI device should only be instantiated for the
> machine types >= 10.0, but not for the older machine types, e.g. by
> introducing a "use-cpi" property to the TYPE_SCLP_EVENT_FACILITY (set
> to true by default). Then in ccw_machine_9_2_class_options(), make
> sure that this property gets switched to "off" again, so that older
> machine types don't have the new TYPE_SCLP_CPI device. WDYT?
> 

I will answer this shortly. Thank you.

>  Thomas

-- 
Mit freundlichen Grüßen / Kind regards
Shalini Chellathurai Saroja
Software Developer
Linux on IBM Z & KVM Development
IBM Deutschland Research & Development GmbH
Dept 1419, Schoenaicher Str. 220, 71032 Boeblingen
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