Re: [Qemu-devel] [Qemu-stable] [PATCH] target-i386: Support migratable=no properly

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting Eduardo Habkost (2014-08-21 15:14:38)
> Forgot to add qemu-devel to "To:". Adding it.
> 
> On Wed, Aug 20, 2014 at 05:30:12PM -0300, Eduardo Habkost wrote:
> > When the "migratable" property was implemented, the behavior was tested
> > by changing the default on the code, but actually using the option on
> > the command-line (e.g. "-cpu host,migratable=false") doesn't work as
> > expected. This is a regression for a common use case of "-cpu host",
> > which is to enable features that are supported by the host CPU + kernel
> > before feature-specific code is added to QEMU.
> > 
> > Fix this by initializing the feature words for "-cpu host" on
> > x86_cpu_parse_featurestr(), right after parsing the CPU options.
> > 
> > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

Ping for stable 2.1.1, freeze is Wednesday.

Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>

> > ---
> > I was considering a more complex (but less hacky) fix, by introducing an
> > enum FeatureBit { OFF, ON, HOST }, making FeatureWord a 32-element
> > FeatureBit array, and initializing the actual feature bits on
> > x86_cpu_realizefn(). But as this is a patch for qemu-stable, I kept the
> > fix as simple as possible.
> > ---
> >  target-i386/cpu-qom.h |  1 +
> >  target-i386/cpu.c     | 17 ++++++++++++-----
> >  2 files changed, 13 insertions(+), 5 deletions(-)
> > 
> > diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h
> > index 71a1b97..7755466 100644
> > --- a/target-i386/cpu-qom.h
> > +++ b/target-i386/cpu-qom.h
> > @@ -92,6 +92,7 @@ typedef struct X86CPU {
> >      bool enforce_cpuid;
> >      bool expose_kvm;
> >      bool migratable;
> > +    bool host_features;
> >  
> >      /* if true the CPUID code directly forward host cache leaves to the guest */
> >      bool cache_info_passthrough;
> > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > index 6d008ab..c0f8efc 100644
> > --- a/target-i386/cpu.c
> > +++ b/target-i386/cpu.c
> > @@ -1318,18 +1318,18 @@ static void host_x86_cpu_initfn(Object *obj)
> >      X86CPU *cpu = X86_CPU(obj);
> >      CPUX86State *env = &cpu->env;
> >      KVMState *s = kvm_state;
> > -    FeatureWord w;
> >  
> >      assert(kvm_enabled());
> >  
> > +    /* We can't fill the features array here because we don't know yet if
> > +     * "migratable" is true or false.
> > +     */
> > +    cpu->host_features = true;
> > +
> >      env->cpuid_level = kvm_arch_get_supported_cpuid(s, 0x0, 0, R_EAX);
> >      env->cpuid_xlevel = kvm_arch_get_supported_cpuid(s, 0x80000000, 0, R_EAX);
> >      env->cpuid_xlevel2 = kvm_arch_get_supported_cpuid(s, 0xC0000000, 0, R_EAX);
> >  
> > -    for (w = 0; w < FEATURE_WORDS; w++) {
> > -        env->features[w] =
> > -            x86_cpu_get_supported_feature_word(w, cpu->migratable);
> > -    }
> >      object_property_set_bool(OBJECT(cpu), true, "pmu", &error_abort);
> >  }
> >  
> > @@ -1828,6 +1828,13 @@ static void x86_cpu_parse_featurestr(CPUState *cs, char *features,
> >          featurestr = strtok(NULL, ",");
> >      }
> >  
> > +    if (cpu->host_features) {
> > +        for (w = 0; w < FEATURE_WORDS; w++) {
> > +            env->features[w] =
> > +                x86_cpu_get_supported_feature_word(w, cpu->migratable);
> > +        }
> > +    }
> > +
> >      for (w = 0; w < FEATURE_WORDS; w++) {
> >          env->features[w] |= plus_features[w];
> >          env->features[w] &= ~minus_features[w];
> > -- 
> > 1.9.3
> > 
> 
> -- 
> Eduardo