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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.08.14 at 18:09, <Paul.Durrant@xxxxxxxxxx> wrote:
>>  -----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.

Or perhaps rather than an ugly cast, just use 1000ULL?

Jan

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