Re: [Qemu-devel] [PATCH v4 2/3] target-i386: add migration support for Intel LMCE

[Paolo Bonzini]

On 16/06/2016 12:29, Haozhong Zhang wrote:
> On 06/16/16 11:51, Paolo Bonzini wrote:
>>
>>
>> On 16/06/2016 08:06, Haozhong Zhang wrote:
>>> Migration is only allowed between VCPUs with the same lmce option.
>>>
>>> Signed-off-by: Haozhong Zhang <address@hidden>
>>> ---
>>>  target-i386/machine.c | 25 +++++++++++++++++++++++++
>>>  1 file changed, 25 insertions(+)
>>>
>>> diff --git a/target-i386/machine.c b/target-i386/machine.c
>>> index cb9adf2..00375a3 100644
>>> --- a/target-i386/machine.c
>>> +++ b/target-i386/machine.c
>>> @@ -347,6 +347,12 @@ static int cpu_post_load(void *opaque, int version_id)
>>>          return -EINVAL;
>>>      }
>>>  
>>> +    if (!cpu->enable_lmce && (env->mcg_cap & MCG_LMCE_P)) {
>>> +        error_report("Config mismatch: VCPU has LMCE enabled, "
>>> +                     "but \"lmce\" option is disabled");
>>> +        return -EINVAL;
>>> +    }
>>> +
>>
>> I think this is unnecessary.  Apart from this, the patch is good and can
>> be squashed in patch 1 for v5.
>>
> 
> Without this check, the migration from LMCE enabled QEMU to LMCE
> disabled QEMU will not fail. Is such configuration change considered
> be error? If not, I will remove the error report and return, but add a
> fix to remove MCG_LMCE_P from env->mcg_cap in this check.

It's considered a user error.  You can skip the "if" completely.

Paolo

> Haozhong
> 
>>
>>>      /*
>>>       * Real mode guest segments register DPL should be zero.
>>>       * Older KVM version were setting it wrongly.
>>> @@ -896,6 +902,24 @@ static const VMStateDescription vmstate_tsc_khz = {
>>>      }
>>>  };
>>>  
>>> +static bool mcg_ext_ctl_needed(void *opaque)
>>> +{
>>> +    X86CPU *cpu = opaque;
>>> +    CPUX86State *env = &cpu->env;
>>> +    return cpu->enable_lmce && env->mcg_ext_ctl;
>>> +}
>>> +
>>> +static const VMStateDescription vmstate_mcg_ext_ctl = {
>>> +    .name = "cpu/mcg_ext_ctl",
>>> +    .version_id = 1,
>>> +    .minimum_version_id = 1,
>>> +    .needed = mcg_ext_ctl_needed,
>>> +    .fields = (VMStateField[]) {
>>> +        VMSTATE_UINT64(env.mcg_ext_ctl, X86CPU),
>>> +        VMSTATE_END_OF_LIST()
>>> +    }
>>> +};
>>> +
>>>  VMStateDescription vmstate_x86_cpu = {
>>>      .name = "cpu",
>>>      .version_id = 12,
>>> @@ -1022,6 +1046,7 @@ VMStateDescription vmstate_x86_cpu = {
>>>  #ifdef TARGET_X86_64
>>>          &vmstate_pkru,
>>>  #endif
>>> +        &vmstate_mcg_ext_ctl,
>>>          NULL
>>>      }
>>>  };
>>>