Re: [Qemu-devel] [PATCH v4 3/3] x86: define a new MSR based feature word -- FEATURE_WORDS_ARCH_CAPABILITIES

[Robert Hoo]

On Thu, 2018-09-20 at 00:13 -0300, Eduardo Habkost wrote:
> On Sun, Sep 02, 2018 at 07:46:07PM +0800, Robert Hoo wrote:
> > Note RSBA is specially treated -- no matter host support it or not,
> > qemu
> > pretends it is supported.
> > 
> > Signed-off-by: Robert Hoo <address@hidden>
> > ---
> >  target/i386/cpu.c | 27 ++++++++++++++++++++++++++-
> >  target/i386/cpu.h | 12 ++++++++++++
> >  2 files changed, 38 insertions(+), 1 deletion(-)
> > 
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 0160e97..8ec9613 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -1129,6 +1129,24 @@ static FeatureWordInfo
> > feature_word_info[FEATURE_WORDS] = {
> >              .reg = R_EDX, },
> >          .tcg_features = ~0U,
> >      },
> > +    /*Below are MSR exposed features*/
> > +    [FEATURE_WORDS_ARCH_CAPABILITIES] = {
> > +        .type = MSR_FEATURE_WORD,
> > +        .feat_names = {
> > +            "rdctl-no", "ibrs-all", "rsba", NULL,
> > +            "ssb-no", NULL, NULL, NULL,
> > +            NULL, NULL, NULL, NULL,
> > +            NULL, NULL, NULL, NULL,
> > +            NULL, NULL, NULL, NULL,
> > +            NULL, NULL, NULL, NULL,
> > +            NULL, NULL, NULL, NULL,
> > +            NULL, NULL, NULL, NULL,
> > +        },
> > +        .msr = { .index = MSR_IA32_ARCH_CAPABILITIES,
> > +                .cpuid_dep = { FEAT_7_0_EDX,
> > +                    CPUID_7_0_EDX_ARCH_CAPABILITIES }
> > +                },
> > +    },
> 
> One critical piece of the code seems to be missing: where exactly
> is the MSR value being set on the VCPU before it runs?
> 
I don't quite understand. Isn't such feature MSR read-only, like CPUID,
simply to enumerate features?
> 
> >  };
> >  
> >  typedef struct X86RegisterInfo32 {
> > @@ -3680,7 +3698,14 @@ static uint32_t
> > x86_cpu_get_supported_feature_word(FeatureWord w,
> >                                                  wi->cpuid.reg);
> >              break;
> >          case MSR_FEATURE_WORD:
> > -            r = kvm_arch_get_supported_msr_feature(kvm_state,
> > +            /* Special case:
> > +             * No matter host status, IA32_ARCH_CAPABILITIES.RSBA
> > [bit 2]
> > +             * is always supported in guest.
> > +             */
> > +            if (wi->msr.index == MSR_IA32_ARCH_CAPABILITIES) {
> > +                r = MSR_ARCH_CAP_RSBA;
> > +            }
> > +            r |= kvm_arch_get_supported_msr_feature(kvm_state,
> >                          wi->msr.index);
> >              break;
> >          }
> > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > index b572a8e..9662730 100644
> > --- a/target/i386/cpu.h
> > +++ b/target/i386/cpu.h
> > @@ -502,9 +502,14 @@ typedef enum FeatureWord {
> >      FEAT_6_EAX,         /* CPUID[6].EAX */
> >      FEAT_XSAVE_COMP_LO, /* CPUID[EAX=0xd,ECX=0].EAX */
> >      FEAT_XSAVE_COMP_HI, /* CPUID[EAX=0xd,ECX=0].EDX */
> > +    FEATURE_WORDS_NUM_CPUID,
> > +    FEATURE_WORDS_FIRST_MSR = FEATURE_WORDS_NUM_CPUID,
> > +    FEATURE_WORDS_ARCH_CAPABILITIES = FEATURE_WORDS_FIRST_MSR,
> >      FEATURE_WORDS,
> >  } FeatureWord;
> >  
> > +#define FEATURE_WORDS_NUM_MSRS (FEATURE_WORDS -
> > FEATURE_WORDS_FIRST_MSR)
> 
> I don't see FEATURE_WORDS_NUM_CPUID, FEATURE_WORDS_FIRST_MS and
> FEATURE_WORDS_NUM_MSRS being used anywhere.  Why are they being
> introduced?
> 
Get rid of them in v5.
> 
> > +
> >  typedef uint32_t FeatureWordArray[FEATURE_WORDS];
> >  
> >  /* cpuid_features bits */
> > @@ -730,6 +735,13 @@ typedef uint32_t
> > FeatureWordArray[FEATURE_WORDS];
> >  #define CPUID_TOPOLOGY_LEVEL_SMT      (1U << 8)
> >  #define CPUID_TOPOLOGY_LEVEL_CORE     (2U << 8)
> >  
> > +/* MSR Feature Bits */
> > +#define MSR_ARCH_CAP_RDCL_NO    (1U << 0)
> > +#define MSR_ARCH_CAP_IBRS_ALL   (1U << 1)
> > +#define MSR_ARCH_CAP_RSBA       (1U << 2)
> > +#define MSR_ARCH_CAP_SKIP_L1DFL_VMENTRY (1U << 3)
> > +#define MSR_ARCH_CAP_SSB_NO     (1U << 4)
> > +
> >  #ifndef HYPERV_SPINLOCK_NEVER_RETRY
> >  #define HYPERV_SPINLOCK_NEVER_RETRY             0xFFFFFFFF
> >  #endif
> > -- 
> > 1.8.3.1
> > 
> > 
> 
>