Re: [Xen-devel] [PATCH 2/2] x86/xen: use capabilities instead of fake cpuid values

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 02/17/2017 09:19 AM, Juergen Gross wrote:
> On 17/02/17 15:05, Boris Ostrovsky wrote:
> > On 02/17/2017 02:36 AM, Juergen Gross wrote:
> > > When running as pv domain xen_cpuid() is being used instead of
> > > native_cpuid(). In xen_cpuid() the aperf/mperf feature is indicated
> > > as not being present by special casing the related cpuid leaf.
> > >
> > > Instead of delivering fake cpuid values clear the cpu capability bit
> > > for aperf/mperf instead.
> > >
> > > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > > ---
> > >  arch/x86/xen/enlighten.c | 11 +++--------
> > >  1 file changed, 3 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > > index 83399ce..0eebb75 100644
> > > --- a/arch/x86/xen/enlighten.c
> > > +++ b/arch/x86/xen/enlighten.c
> > > @@ -301,9 +301,6 @@ xen_running_on_version_or_later(unsigned int
> > > major, unsigned int minor)
> > >      return false;
> > >  }
> > >
> > > -#define CPUID_THERM_POWER_LEAF 6
> > > -#define APERFMPERF_PRESENT 0
> > > -
> > >  static __read_mostly unsigned int cpuid_leaf1_edx_mask = ~0;
> > >  static __read_mostly unsigned int cpuid_leaf1_ecx_mask = ~0;
> > >
> > > @@ -337,11 +334,6 @@ static void xen_cpuid(unsigned int *ax, unsigned
> > > int *bx,
> > >          *dx = cpuid_leaf5_edx_val;
> > >          return;
> > >
> > > -    case CPUID_THERM_POWER_LEAF:
> > > -        /* Disabling APERFMPERF for kernel usage */
> > > -        maskecx = ~(1 << APERFMPERF_PRESENT);
> > > -        break;
> > > -
> >
> > But now APERF/MPERF will be reported as supported by CPUID, won't it?
> Yes. But this shouldn't be a problem as the kernel is always testing
> X86_FEATURE_APERFMPERF for testing the support.

But X86_FEATURE_APERFMPERF cap is set based on CPUID query.

-boris

> > >      case 0xb:
> > >          /* Suppress extended topology stuff */
> > >          maskebx = 0;
> > > @@ -462,6 +454,9 @@ static void __init xen_init_cpuid_mask(void)
> > >      if (xen_check_mwait())
> > >          cpuid_leaf1_ecx_set_mask = (1 << (X86_FEATURE_MWAIT % 32));
> > >
> > > +    /* Disable APERFMPERF feature. */
> > > +    setup_clear_cpu_cap(X86_FEATURE_APERFMPERF);
> > > +
> > >      /* Disable DCA feature. */
> > >      setup_clear_cpu_cap(X86_FEATURE_DCA);
> >
> > I think both of those can go to xen_set_cpu_features().
> Okay. I'll move them.
>
> I think we can convert some of the remaining cpuid bit modifications to
> cpu capabilities as well.
>
>
> Juergen
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