Re: [PATCH v11 15/16] s390x/pci: Implement migration for emulated devices

[Konstantin Shkolnyy <kshk@linux.ibm.com>]

On 261005 17:20, Farhan Ali wrote:
> <..snip..>
> 
> On 9/30/2026 7:52 AM, Konstantin Shkolnyy wrote:
>> +/*
>> + * When pending_sei load is executed, pending_sei can already contain 
>> SEIs
>> + * generated here in the target QEMU, for example, by state loads of 
>> zpci
>> + * devices. A dumb load here would place the older SEIs from the 
>> source QEMU
>> + * after the new SEIs. To fix this, we have pre_load() stash the new 
>> SEIs from
>> + * pending_sei and post_load() unstash them after the old ones.
>> + */
>> +static void s390_pci_move_sei_list(SeiContainerList *dst, 
>> SeiContainerList *src)
>> +{
>> +    SeiContainer *sei_cont;
>> +
>> +    while ((sei_cont = QTAILQ_FIRST(src))) {
>> +        QTAILQ_REMOVE(src, sei_cont, link);
>> +        QTAILQ_INSERT_TAIL(dst, sei_cont, link);
>> +    }
>> +}
>> +
>> +static int s390_pcihost_pending_sei_vmstate_pre_load(void *opaque)
>> +{
>> +    S390pciState *s = S390_PCI_HOST_BRIDGE(opaque);
>> +
>> +    QTAILQ_INIT(&s->pending_sei_stash);
>> +    s390_pci_move_sei_list(&s->pending_sei_stash, &s->pending_sei);
>> +    return 0;
>> +}
> 
> Does this mean we can append SEIs to the list while we are still 
> migrating? In that case do we need any form of synchronization here when 
> accessing the pending_sei list?

SEIs can be generated the migration process itself - by 
s390_pci_ioat_replay() called from s390_pci_device_post_load_errp().
That happens before the migration process comes here to load 
s390_pcihost state (with old SEIs).

Since the migration process is single-threaded I don't think we need to 
synchronize between its stages.

> 
> Thanks
> 
> Farhan
> 
>> +
>> +static int s390_pcihost_pending_sei_vmstate_post_load(void *opaque,
>> +                                                      int version_id)
>> +{
>> +    S390pciState *s = S390_PCI_HOST_BRIDGE(opaque);
>> +
>> +    s390_pci_move_sei_list(&s->pending_sei, &s->pending_sei_stash);
>> +    return 0;
>> +}
>> +
>> +static const VMStateDescription s390_pcihost_pending_sei_vmstate = {
>> +    .name = TYPE_S390_PCI_HOST_BRIDGE "/pending-sei",
>> +    .version_id = 1,
>> +    .minimum_version_id = 1,
>> +    .needed = s390_pcihost_pending_sei_vmstate_needed,
>> +    .pre_load = s390_pcihost_pending_sei_vmstate_pre_load,
>> +    .post_load = s390_pcihost_pending_sei_vmstate_post_load,
>> +    .fields = (const VMStateField[]) {
>> +        VMSTATE_QTAILQ_V(pending_sei, S390pciState, 1,
>> +                         vmstate_sei_container, SeiContainer, link),
>> +        VMSTATE_END_OF_LIST()
>> +    }
>> +};
>> +