Re: [PATCH v2 2/3] target/loongarch: migrate pv_features in the vCPU VMState

[Tao Cui <cui.tao@linux.dev>]

在 2026/7/10 11:15, Bibo Mao 写道:
> 
> 
> On 2026/7/10 上午11:02, Bibo Mao wrote:
>>
>>
>> On 2026/7/10 上午8:50, Tao Cui wrote:
>>> From: Tao Cui <cuitao@kylinos.cn>
>>>
>>> pv_features holds the value of pseudo-register CPUCFG_KVM_FEATURE and is now
>>> pushed per vCPU. Add it to the vCPU VMState as a subsection (sent when
>>> non-zero) so it travels with the vCPU across migration between host kernel
>>> versions.
>>>
>>> Signed-off-by: Tao Cui <cuitao@kylinos.cn>
>>> ---
>>>   target/loongarch/machine.c | 19 +++++++++++++++++++
>>>   1 file changed, 19 insertions(+)
>>>
>>> diff --git a/target/loongarch/machine.c b/target/loongarch/machine.c
>>> index 931a5ca5ba..b8819bd44d 100644
>>> --- a/target/loongarch/machine.c
>>> +++ b/target/loongarch/machine.c
>>> @@ -65,6 +65,24 @@ static const VMStateDescription vmstate_msgint = {
>>>       },
>>>   };
>>> +static bool pv_features_needed(void *opaque)
>>> +{
>>> +    LoongArchCPU *cpu = opaque;
>>> +
>>> +    return cpu->env.pv_features != 0;
>> I think cpu->no_pv_feature should be check here. For QEMU 11.1 pv_feature is not supported for migration, for later version it supports, something like this:
>>         return !cpu->no_pv_feature;
> For successful migration, env.pv_features from source host should be subset of destination host, there should be such checking also.
> 
Agreed on both points.

1. I'll change .needed to `return !cpu->no_pv_feature` so the subsection
   is gated by machine version. Since it references no_pv_feature (added
   in the compat patch), I'll reorder so compat comes before vmstate.

2. For the subset check, I'll add a .post_load that calls
   kvm_feature_supported() for each PV feature to build the destination's
   supported mask, and rejects migration if the migrated pv_features has
   bits outside it. Does this look right?

Thanks,
Tao
>>
>> Regards
>> Bibo Mao
>>> +}
>>> +
>>> +static const VMStateDescription vmstate_pv_features = {
>>> +    .name = "cpu/pv_features",
>>> +    .version_id = 1,
>>> +    .minimum_version_id = 1,
>>> +    .needed = pv_features_needed,
>>> +    .fields = (const VMStateField[]) {
>>> +        VMSTATE_UINT32(env.pv_features, LoongArchCPU),
>>> +        VMSTATE_END_OF_LIST()
>>> +    },
>>> +};
>>> +
>>>   static const VMStateDescription vmstate_lsxh_reg = {
>>>       .name = "lsxh_reg",
>>>       .version_id = 1,
>>> @@ -289,6 +307,7 @@ const VMStateDescription vmstate_loongarch_cpu = {
>>>           &vmstate_lbt,
>>>           &vmstate_msgint,
>>>           &vmstate_pmu,
>>> +        &vmstate_pv_features,
>>>           NULL
>>>       }
>>>   };
>>>
>>
>