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

[Haozhong Zhang]

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.

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
> >      }
> >  };
> >