Re: [Xen-devel] [PATCH v7 2/2] x86/viridian: Add partition time reference counter MSR support

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 27 August 2014 17:02
> To: Paul Durrant
> Cc: Christoph Egger; Ian Campbell; Ian Jackson; Stefano Stabellini; xen-
> devel@xxxxxxxxxxxxx; Keir (Xen.org)
> Subject: Re: [PATCH v7 2/2] x86/viridian: Add partition time reference
> counter MSR support
> 
> >>> On 27.08.14 at 17:44, <paul.durrant@xxxxxxxxxx> wrote:
> > This patch optionally re-instates support for the partition time reference
> > counter that was previously introduced by commit
> > e36cd2cdc9674a7a4855d21fb7b3e6e17c4bb33b and reverted by commit
> > 1cd4fab14ce25859efa4a2af13475e6650a5506c. The previous
> implementation was
> > non-optional and flawed.
> >
> > This implementation uses the tsc of vcpu0, which is preserved across
> > save/restore as part of the architectural state, and then converts that
> > to a 100ns tick using the domain's tsc_khz.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> > Cc: Keir Fraser <keir@xxxxxxx>
> > Cc: Jan Beulich <jbeulich@xxxxxxxx>
> > Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > Cc: Christoph Egger <chegger@xxxxxxxxx>
> > ---
> >  docs/man/xl.cfg.pod.5            |    7 +++++++
> >  tools/libxl/libxl_dom.c          |    3 +++
> >  tools/libxl/libxl_types.idl      |    1 +
> >  xen/arch/x86/hvm/viridian.c      |   28 +++++++++++++++++++++++-----
> >  xen/arch/x86/time.c              |    4 ++--
> >  xen/include/asm-x86/perfc_defn.h |    1 +
> >  xen/include/asm-x86/time.h       |    4 ++++
> >  xen/include/public/hvm/params.h  |    9 ++++++++-
> >  8 files changed, 49 insertions(+), 8 deletions(-)
> >
> > diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
> > index d91f101..ac3798a 100644
> > --- a/docs/man/xl.cfg.pod.5
> > +++ b/docs/man/xl.cfg.pod.5
> > @@ -1131,6 +1131,13 @@ This set incorporates the TSC and APIC
> frequency MSRs.
> >  This enlightenment can improve performance of Windows 7 and Windows
> >  Server 2008 R2 onwards.
> >
> > +=item B<time_ref_count>
> > +
> > +This set incorporates Partition Time Reference Counter MSR.
> > +
> > +This enlightenment can improve performance of Windows 8 and Windows
> > +Server 2012 onwards.
> > +
> >  =back
> >
> >  See the latest version of Microsoft's Hypervisor Top-Level Functional
> > diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
> > index e854984..579188a 100644
> > --- a/tools/libxl/libxl_dom.c
> > +++ b/tools/libxl/libxl_dom.c
> > @@ -241,6 +241,9 @@ static void hvm_set_viridian_features(libxl__gc *gc,
> > uint32_t domid,
> >              case LIBXL_VIRIDIAN_ENLIGHTENMENT_FREQ:
> >                  feature_mask &= ~HVMPV_no_freq;
> >                  break;
> > +            case LIBXL_VIRIDIAN_ENLIGHTENMENT_TIME_REF_COUNT:
> > +                feature_mask |= HVMPV_time_ref_count;
> > +                break;
> >              default:
> >                  LIBXL__LOG(CTX, LIBXL__LOG_WARNING,
> >                             "Unknown viridian enlightenment %d\n",
> > diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
> > index 3b0059c..a2a523e 100644
> > --- a/tools/libxl/libxl_types.idl
> > +++ b/tools/libxl/libxl_types.idl
> > @@ -183,6 +183,7 @@ libxl_viridian_enlightenment =
> > Enumeration("viridian_enlightenment", [
> >      (0, "unknown"),
> >      (1, "base"),
> >      (2, "freq"),
> > +    (3, "time_ref_count"),
> >      ])
> >
> >  #
> > diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
> > index 28c4479..04cd158 100644
> > --- a/xen/arch/x86/hvm/viridian.c
> > +++ b/xen/arch/x86/hvm/viridian.c
> > @@ -36,11 +36,11 @@
> >  #define HvNotifyLongSpinWait    8
> >
> >  /* Viridian CPUID 4000003, Viridian MSR availability. */
> > -#define CPUID3A_MSR_REF_COUNT   (1 << 1)
> > -#define CPUID3A_MSR_APIC_ACCESS (1 << 4)
> > -#define CPUID3A_MSR_HYPERCALL   (1 << 5)
> > -#define CPUID3A_MSR_VP_INDEX    (1 << 6)
> > -#define CPUID3A_MSR_FREQ        (1 << 11)
> > +#define CPUID3A_MSR_TIME_REF_COUNT (1 << 1)
> > +#define CPUID3A_MSR_APIC_ACCESS    (1 << 4)
> > +#define CPUID3A_MSR_HYPERCALL      (1 << 5)
> > +#define CPUID3A_MSR_VP_INDEX       (1 << 6)
> > +#define CPUID3A_MSR_FREQ           (1 << 11)
> >
> >  /* Viridian CPUID 4000004, Implementation Recommendations. */
> >  #define CPUID4A_MSR_BASED_APIC  (1 << 3)
> > @@ -93,6 +93,8 @@ int cpuid_viridian_leaves(unsigned int leaf, unsigned
> int
> > *eax,
> >                  CPUID3A_MSR_VP_INDEX);
> >          if ( !(viridian_feature_mask(d) & HVMPV_no_freq) )
> >              *eax |= CPUID3A_MSR_FREQ;
> > +        if ( viridian_feature_mask(d) & HVMPV_time_ref_count )
> > +            *eax |= CPUID3A_MSR_TIME_REF_COUNT;
> >          break;
> >      case 4:
> >          /* Recommended hypercall usage. */
> > @@ -344,6 +346,22 @@ int rdmsr_viridian_regs(uint32_t idx, uint64_t *val)
> >          *val = v->arch.hvm_vcpu.viridian.apic_assist.raw;
> >          break;
> >
> > +    case VIRIDIAN_MSR_TIME_REF_COUNT:
> > +    {
> > +        uint64_t tsc;
> > +        struct time_scale tsc_to_ns;
> > +
> > +        if ( !(viridian_feature_mask(d) & HVMPV_time_ref_count) )
> > +            return 0;
> > +
> > +        perfc_incr(mshv_rdmsr_time_ref_count);
> > +        tsc = hvm_get_guest_tsc(pt_global_vcpu_target(d));
> > +
> > +        /* convert tsc to count of 100ns periods */
> > +        set_time_scale(&tsc_to_ns, d->arch.tsc_khz * 1000);
> 
> While the second parameter of the function has type u64, nothing
> forces the multiplication to be done at 64-bit width (and 4GHz or
> beyond clock speed isn't plain impossible).
> 

True. The promotion will probably done afterwards; I'll add a cast to make sure 
it's done before.

> > +        *val = scale_delta(tsc, &tsc_to_ns) / 100ul;
> > +        break;
> > +    }
> >      default:
> 
> I'm pretty sure I asked for a blank line to be added between the
> closing brace and the default: before.

Oh, sorry. I'll add that.

  Paul

> 
> Jan

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