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Re: [Qemu-devel] [PATCH 3/7] i386: Add spec-ctrl CPUID bit


From: Gonglei (Arei)
Subject: Re: [Qemu-devel] [PATCH 3/7] i386: Add spec-ctrl CPUID bit
Date: Tue, 16 Jan 2018 14:50:29 +0000

> -----Original Message-----
> From: Eduardo Habkost [mailto:address@hidden
> Sent: Monday, January 15, 2018 8:23 PM
> To: Gonglei (Arei)
> Cc: address@hidden; Paolo Bonzini
> Subject: Re: [Qemu-devel] [PATCH 3/7] i386: Add spec-ctrl CPUID bit
> 
> On Sat, Jan 13, 2018 at 03:04:44AM +0000, Gonglei (Arei) wrote:
> >
> > > -----Original Message-----
> > > From: Qemu-devel
> > > [mailto:address@hidden On
> > > Behalf Of Eduardo Habkost
> > > Sent: Tuesday, January 09, 2018 11:45 PM
> > > To: address@hidden
> > > Cc: Paolo Bonzini
> > > Subject: [Qemu-devel] [PATCH 3/7] i386: Add spec-ctrl CPUID bit
> > >
> > > Add the feature name and a CPUID_7_0_EDX_SPEC_CTRL macro.
> > >
> > > Signed-off-by: Eduardo Habkost <address@hidden>
> > > ---
> > >  target/i386/cpu.h | 1 +
> > >  target/i386/cpu.c | 2 +-
> > >  2 files changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > > index 07f47997d6..de387c1311 100644
> > > --- a/target/i386/cpu.h
> > > +++ b/target/i386/cpu.h
> > > @@ -667,6 +667,7 @@ typedef uint32_t
> > > FeatureWordArray[FEATURE_WORDS];
> > >
> > >  #define CPUID_7_0_EDX_AVX512_4VNNIW (1U << 2) /* AVX512 Neural
> > > Network Instructions */
> > >  #define CPUID_7_0_EDX_AVX512_4FMAPS (1U << 3) /* AVX512 Multiply
> > > Accumulation Single Precision */
> > > +#define CPUID_7_0_EDX_SPEC_CTRL     (1U << 26) /* Speculation
> Control
> > > */
> > >
> > >  #define CPUID_XSAVE_XSAVEOPT   (1U << 0)
> > >  #define CPUID_XSAVE_XSAVEC     (1U << 1)
> > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > > index 9f4f949899..1be1642eb2 100644
> > > --- a/target/i386/cpu.c
> > > +++ b/target/i386/cpu.c
> > > @@ -459,7 +459,7 @@ static FeatureWordInfo
> > > feature_word_info[FEATURE_WORDS] = {
> > >              NULL, NULL, NULL, NULL,
> > >              NULL, NULL, NULL, NULL,
> > >              NULL, NULL, NULL, NULL,
> > > -            NULL, NULL, NULL, NULL,
> > > +            NULL, NULL, "spec-ctrl", NULL,
> > >              NULL, NULL, NULL, NULL,
> > >          },
> > >          .cpuid_eax = 7,
> > > --
> > > 2.14.3
> > >
> > Don't we need to pass-through cupid_7_edx to guest when configuring '-cpu
> host'?
> > Otherwise how guests use IBPB/IBRS/STIPB capabilities?
> 
> We already do.  See the check for cpu->max_features at
> x86_cpu_expand_features().
> 
> Do you see something else missing?
> 
No, thank you. My bad. :(

Thanks,
-Gonglei




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