Re: [PATCH v5 3/3] x86/viridian: Add partition time reference counter MSR support

["Egger, Christoph" <chegger@amazon.de>]

On 05.08.14 15:07, Paul Durrant 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@citrix.com>
> Cc: Keir Fraser <keir@xen.org>
> Cc: Jan Beulich <jbeulich@suse.com>
> Cc: Ian Campbell <ian.campbell@citrix.com>
> Cc: Ian Jackson <ian.jackson@eu.citrix.com>
> Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> ---
>  docs/man/xl.cfg.pod.5            |    7 +++++++
>  tools/libxl/libxl_dom.c          |    2 ++
>  xen/arch/x86/hvm/viridian.c      |   24 +++++++++++++++++++-----
>  xen/include/asm-x86/perfc_defn.h |    1 +
>  xen/include/public/hvm/params.h  |    9 ++++++++-
>  5 files changed, 37 insertions(+), 6 deletions(-)
> 
> diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
> index a05e831..e4692982 100644
> --- a/docs/man/xl.cfg.pod.5
> +++ b/docs/man/xl.cfg.pod.5
> @@ -1109,6 +1109,13 @@ 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 cc57931..224a4d9 100644
> --- a/tools/libxl/libxl_dom.c
> +++ b/tools/libxl/libxl_dom.c
> @@ -222,6 +222,8 @@ static void hvm_set_viridian_features(libxl__gc *gc, uint32_t domid,
>              feature_mask |= HVMPV_base_freq;
>          else if (strcmp(*p, "freq") == 0)
>              feature_mask &= ~HVMPV_no_freq;
> +        else if (strcmp(*p, "time-ref-count") == 0)
> +            feature_mask |= HVMPV_time_ref_count;
>          p++;
>      }
>  
> diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
> index 6fcfa96..5e99af2 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. */
> @@ -349,6 +351,18 @@ 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;
> +
> +        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));
> +        *val = (tsc * 10000ull) / d->arch.tsc_khz;

This is correct by math but not in implementation.
You need to stay within 64bits. Please add the math formula
in a comment.

Christoph

> +        break;
> +    }
>      default:
>          return 0;
>      }
> diff --git a/xen/include/asm-x86/perfc_defn.h b/xen/include/asm-x86/perfc_defn.h
> index 7d802cc..170da00 100644
> --- a/xen/include/asm-x86/perfc_defn.h
> +++ b/xen/include/asm-x86/perfc_defn.h
> @@ -120,6 +120,7 @@ PERFCOUNTER(mshv_rdmsr_hc_page,         "MS Hv rdmsr hypercall page")
>  PERFCOUNTER(mshv_rdmsr_vp_index,        "MS Hv rdmsr vp index")
>  PERFCOUNTER(mshv_rdmsr_tsc_frequency,   "MS Hv rdmsr TSC frequency")
>  PERFCOUNTER(mshv_rdmsr_apic_frequency,  "MS Hv rdmsr APIC frequency")
> +PERFCOUNTER(mshv_rdmsr_time_ref_count,  "MS Hv rdmsr time ref count")
>  PERFCOUNTER(mshv_rdmsr_icr,             "MS Hv rdmsr icr")
>  PERFCOUNTER(mshv_rdmsr_tpr,             "MS Hv rdmsr tpr")
>  PERFCOUNTER(mshv_rdmsr_apic_assist,     "MS Hv rdmsr APIC assist")
> diff --git a/xen/include/public/hvm/params.h b/xen/include/public/hvm/params.h
> index 68d26fd..3c51072 100644
> --- a/xen/include/public/hvm/params.h
> +++ b/xen/include/public/hvm/params.h
> @@ -88,7 +88,14 @@
>  #define _HVMPV_no_freq 1
>  #define HVMPV_no_freq  (1 << _HVMPV_no_freq)
>  
> -#define HVMPV_feature_mask (HVMPV_base_freq|HVMPV_no_freq)
> +/* Enable Partition Time Reference Counter (HV_X64_MSR_TIME_REF_COUNT) */
> +#define _HVMPV_time_ref_count 2
> +#define HVMPV_time_ref_count  (1 << _HVMPV_time_ref_count)
> +
> +#define HVMPV_feature_mask \
> +	(HVMPV_base_freq | \
> +	 HVMPV_no_freq | \
> +	 HVMPV_time_ref_count)
>  
>  #endif
>  
>