Re: [Qemu-devel] [RFC untested PATCH] i386/cpu: make -cpu host support monitor/mwait

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 12, 2018 at 02:56:05PM +0200, Igor Mammedov wrote:
> On Fri, 8 Jun 2018 23:59:19 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > When guest CPU PM is enabled, and with -cpu host, expose the host CPU
> > MWAIT leaf to guest so guest can make good PM decisions.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 
> > This builds but is untested. Is this a reasonable way to go about it?
> > 
> >  target/i386/cpu.h |  9 +++++++++
> >  target/i386/cpu.c | 18 +++++++++++++-----
> >  2 files changed, 22 insertions(+), 5 deletions(-)
> > 
> > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > index 664504610e..309f804573 100644
> > --- a/target/i386/cpu.h
> > +++ b/target/i386/cpu.h
> > @@ -1378,6 +1378,15 @@ struct X86CPU {
> >      /* if true the CPUID code directly forward host cache leaves to the guest */
> >      bool cache_info_passthrough;
> >  
> > +    /* if true the CPUID code directly forwards
> > +     * host monitor/mwait leaves to the guest */
> > +    struct {
> > +        uint32_t eax;
> > +        uint32_t ebx;
> > +        uint32_t ecx;
> > +        uint32_t edx;
> > +    } mwait;
> > +
> >      /* Features that were filtered out because of missing host capabilities */
> >      uint32_t filtered_features[FEATURE_WORDS];
> >  
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 94260412e2..a49443de56 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -3760,11 +3760,11 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
> >          }
> >          break;
> >      case 5:
> > -        /* mwait info: needed for Core compatibility */
> > -        *eax = 0; /* Smallest monitor-line size in bytes */
> > -        *ebx = 0; /* Largest monitor-line size in bytes */
> > -        *ecx = CPUID_MWAIT_EMX | CPUID_MWAIT_IBE;
> > -        *edx = 0;
> > +        /* MONITOR/MWAIT Leaf */
> > +        *eax = cpu->mwait.eax; /* Smallest monitor-line size in bytes */
> > +        *ebx = cpu->mwait.ebx; /* Largest monitor-line size in bytes */
> > +        *ecx = cpu->mwait.ecx; /* flags */
> > +        *edx = cpu->mwait.edx; /* mwait substates */
> >          break;
> >      case 6:
> >          /* Thermal and Power Leaf */
> > @@ -4595,6 +4595,14 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
> >          goto out;
> >      }
> >  
> > +    if (xcc->host_cpuid_required && enable_cpu_pm) {
> > +        host_cpuid(5, 0, &cpu->mwait.eax, &cpu->mwait.ebx,
> > +                   &cpu->mwait.ecx, &cpu->mwait.edx);
> > +    }
> could this state be migrated? or 'host' is still unmigratable?

Host is still unmigratable.

> also max_x86_cpu_initfn() might be better place for filling it up.
> 
> > +    /* We always wake on interrupt even if host does not have the capability */
> > +    /* mwait extended info: needed for Core compatibility */
> > +    cpu->mwait.ecx |= CPUID_MWAIT_EMX | CPUID_MWAIT_IBE;
> > +
> >      if (cpu->apic_id == UNASSIGNED_APIC_ID) {
> >          error_setg(errp, "apic-id property was not initialized properly");
> >          return;