Re: [Xen-devel] [PATCH v2] x86/viridian: Add Partition Reference Time enlightenment

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

Sorry, this should have been v3. I'll re-post.

  Paul

> -----Original Message-----
> From: Paul Durrant [mailto:paul.durrant@xxxxxxxxxx]
> Sent: 13 October 2014 15:24
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Paul Durrant; Keir (Xen.org); Jan Beulich; Ian Campbell; Ian Jackson;
> Stefano Stabellini; Christoph Egger
> Subject: [PATCH v2] x86/viridian: Add Partition Reference Time
> enlightenment
> 
> The presence of the partition reference time enlightenment persuades
> newer
> versions of Windows to prefer the TSC as their primary time source. Hence,
> if rdtsc is not being emulated and is invariant then many vmexits (for
> alternative time sources such as the HPET or reference counter MSR) can
> be avoided.
> 
> The implementation is not yet complete as no attempt is made to prevent
> emulation of rdtsc if the enlightenment is active and guest and host
> TSC frequencies differ. To do that requires invasive changes in the core
> x86 time code and hence a lot more testing.
> 
> This patch avoids the issue by disabling the enlightenment if rdtsc is
> being emulated, causing Windows to choose another time source. This is
> safe, but may cause a big variation in performance of guests migrated
> between hosts of differing TSC frequency. Thus the enlightenment is not
> enabled in the default set, but may be enabled to improve guest
> performance
> where such migrations are not a concern.
> 
> See section 15.4 of the Microsoft Hypervisor Top Level Functional
> Specification v4.0a for details.
> 
> 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>
> ---
> v2:
>  - Prevent TscSequence increment loop from being exposed to a running
>    domain
> 
>  docs/man/xl.cfg.pod.5                  |    6 ++
>  tools/libxl/libxl_dom.c                |    3 +
>  tools/libxl/libxl_types.idl            |    1 +
>  xen/arch/x86/hvm/viridian.c            |  116
> +++++++++++++++++++++++++++++++-
>  xen/include/asm-x86/hvm/viridian.h     |   35 ++++++++++
>  xen/include/public/arch-x86/hvm/save.h |   11 +++
>  xen/include/public/hvm/params.h        |    7 +-
>  7 files changed, 177 insertions(+), 2 deletions(-)
> 
> diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
> index 8bba21c..925adbb 100644
> --- a/docs/man/xl.cfg.pod.5
> +++ b/docs/man/xl.cfg.pod.5
> @@ -1163,6 +1163,12 @@ This group incorporates Partition Time Reference
> Counter MSR. This
>  enlightenment can improve performance of Windows 8 and Windows
>  Server 2012 onwards.
> 
> +=item B<reference_tsc>
> +
> +This set incorporates the Partition Reference TSC MSR. This
> +enlightenment can improve performance of Windows 7 and Windows
> +Server 2008 R2 onwards.
> +
>  =item B<defaults>
> 
>  This is a special value that enables the default set of groups, which
> diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
> index bd21841..d04fc0d 100644
> --- a/tools/libxl/libxl_dom.c
> +++ b/tools/libxl/libxl_dom.c
> @@ -262,6 +262,9 @@ static int hvm_set_viridian_features(libxl__gc *gc,
> uint32_t domid,
>      if (libxl_bitmap_test(&enlightenments,
> LIBXL_VIRIDIAN_ENLIGHTENMENT_TIME_REF_COUNT))
>          mask |= HVMPV_time_ref_count;
> 
> +    if (libxl_bitmap_test(&enlightenments,
> LIBXL_VIRIDIAN_ENLIGHTENMENT_REFERENCE_TSC))
> +        mask |= HVMPV_reference_tsc;
> +
>      if (mask != 0 &&
>          xc_hvm_param_set(CTX->xch,
>                           domid,
> diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
> index 90d152f..da75a40 100644
> --- a/tools/libxl/libxl_types.idl
> +++ b/tools/libxl/libxl_types.idl
> @@ -183,6 +183,7 @@ libxl_viridian_enlightenment =
> Enumeration("viridian_enlightenment", [
>      (0, "base"),
>      (1, "freq"),
>      (2, "time_ref_count"),
> +    (3, "reference_tsc"),
>      ])
> 
>  #
> diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
> index 6726168..528bb8b 100644
> --- a/xen/arch/x86/hvm/viridian.c
> +++ b/xen/arch/x86/hvm/viridian.c
> @@ -21,6 +21,7 @@
>  #define VIRIDIAN_MSR_HYPERCALL                  0x40000001
>  #define VIRIDIAN_MSR_VP_INDEX                   0x40000002
>  #define VIRIDIAN_MSR_TIME_REF_COUNT             0x40000020
> +#define VIRIDIAN_MSR_REFERENCE_TSC              0x40000021
>  #define VIRIDIAN_MSR_TSC_FREQUENCY              0x40000022
>  #define VIRIDIAN_MSR_APIC_FREQUENCY             0x40000023
>  #define VIRIDIAN_MSR_EOI                        0x40000070
> @@ -40,6 +41,7 @@
>  #define CPUID3A_MSR_APIC_ACCESS    (1 << 4)
>  #define CPUID3A_MSR_HYPERCALL      (1 << 5)
>  #define CPUID3A_MSR_VP_INDEX       (1 << 6)
> +#define CPUID3A_MSR_REFERENCE_TSC  (1 << 9)
>  #define CPUID3A_MSR_FREQ           (1 << 11)
> 
>  /* Viridian CPUID 4000004, Implementation Recommendations. */
> @@ -95,6 +97,8 @@ int cpuid_viridian_leaves(unsigned int leaf, unsigned int
> *eax,
>              *eax |= CPUID3A_MSR_FREQ;
>          if ( viridian_feature_mask(d) & HVMPV_time_ref_count )
>              *eax |= CPUID3A_MSR_TIME_REF_COUNT;
> +        if ( viridian_feature_mask(d) & HVMPV_reference_tsc )
> +            *eax |= CPUID3A_MSR_REFERENCE_TSC;
>          break;
>      case 4:
>          /* Recommended hypercall usage. */
> @@ -155,6 +159,17 @@ static void dump_apic_assist(const struct vcpu *v)
>             v, aa->fields.enabled, (unsigned long)aa->fields.pfn);
>  }
> 
> +static void dump_reference_tsc(const struct domain *d)
> +{
> +    const union viridian_reference_tsc *rt;
> +
> +    rt = &d->arch.hvm_domain.viridian.reference_tsc;
> +
> +    printk(XENLOG_G_INFO "d%d: VIRIDIAN REFERENCE_TSC: enabled: %x
> pfn: %lx\n",
> +           d->domain_id,
> +           rt->fields.enabled, (unsigned long)rt->fields.pfn);
> +}
> +
>  static void enable_hypercall_page(struct domain *d)
>  {
>      unsigned long gmfn = d-
> >arch.hvm_domain.viridian.hypercall_gpa.fields.pfn;
> @@ -224,6 +239,81 @@ static void initialize_apic_assist(struct vcpu *v)
>      put_page_and_type(page);
>  }
> 
> +static void update_reference_tsc(struct domain *d, bool_t initialize)
> +{
> +    unsigned long gmfn = d-
> >arch.hvm_domain.viridian.reference_tsc.fields.pfn;
> +    struct page_info *page = get_page_from_gfn(d, gmfn, NULL,
> P2M_ALLOC);
> +    HV_REFERENCE_TSC_PAGE *p;
> +
> +    if ( !page || !get_page_type(page, PGT_writable_page) )
> +    {
> +        if ( page )
> +            put_page(page);
> +        gdprintk(XENLOG_WARNING, "Bad GMFN %lx (MFN %lx)\n", gmfn,
> +                 page ? page_to_mfn(page) : INVALID_MFN);
> +        return;
> +    }
> +
> +    p = __map_domain_page(page);
> +
> +    if ( initialize )
> +        clear_page(p);
> +
> +    /*
> +     * This enlightenment must be disabled is the host TSC is not invariant.
> +     * However it is also disabled if vtsc is true (which means rdtsc is 
> being
> +     * emulated). This generally happens when guest TSC freq and host TSC
> freq
> +     * don't match. The TscScale value could be adjusted to cope with this,
> +     * allowing vtsc to be turned off, but support for this is not yet 
> present
> +     * in the hypervisor. Thus is it is possible that migrating a Windows VM
> +     * between hosts of differing TSC frequencies may result in large
> +     * differences in guest performance.
> +     */
> +    if ( !host_tsc_is_safe() || d->arch.vtsc )
> +    {
> +        /*
> +         * The specification states that valid values of TscSequence range
> +         * from 0 to 0xFFFFFFFE. The value 0xFFFFFFFF is used to indicate
> +         * this mechanism is no longer a reliable source of time and that
> +         * the VM should fall back to a different source.
> +         *
> +         * Server 2012 (6.2 kernel) and 2012 R2 (6.3 kernel) actually violate
> +         * the spec. and rely on a value of 0 to indicate that this
> +         * enlightenment should no longer be used. These two kernel
> +         * versions are currently the only ones to make use of this
> +         * enlightenment, so just use 0 here.
> +         */
> +        p->TscSequence = 0;
> +
> +        printk(XENLOG_G_INFO "d%d: VIRIDIAN REFERENCE_TSC:
> invalidated\n",
> +               d->domain_id);
> +        return;
> +    }
> +
> +    /*
> +     * The guest will calculate reference time according to the following
> +     * formula:
> +     *
> +     * ReferenceTime = ((RDTSC() * TscScale) >> 64) + TscOffset
> +     *
> +     * Windows uses a 100ns tick, so we need a scale which is cpu
> +     * ticks per 100ns shifted left by 64.
> +     */
> +    p->TscScale = ((10000ul << 32) / d->arch.tsc_khz) << 32;
> +
> +    if ( initialize )
> +        p->TscSequence = 1;
> +    else /* guest is paused */
> +        do {
> +            p->TscSequence++;
> +        } while ( p->TscSequence == 0xFFFFFFFF ||
> +                  p->TscSequence == 0 ); /* Avoid both 'invalid' values */
> +
> +    unmap_domain_page(p);
> +
> +    put_page_and_type(page);
> +}
> +
>  int wrmsr_viridian_regs(uint32_t idx, uint64_t val)
>  {
>      struct vcpu *v = current;
> @@ -282,6 +372,17 @@ int wrmsr_viridian_regs(uint32_t idx, uint64_t val)
>              initialize_apic_assist(v);
>          break;
> 
> +    case VIRIDIAN_MSR_REFERENCE_TSC:
> +        if ( !(viridian_feature_mask(d) & HVMPV_reference_tsc) )
> +            return 0;
> +
> +        perfc_incr(mshv_wrmsr_tsc_msr);
> +        d->arch.hvm_domain.viridian.reference_tsc.raw = val;
> +        dump_reference_tsc(d);
> +        if ( d->arch.hvm_domain.viridian.reference_tsc.fields.enabled )
> +            update_reference_tsc(d, 1);
> +        break;
> +
>      default:
>          return 0;
>      }
> @@ -346,6 +447,14 @@ int rdmsr_viridian_regs(uint32_t idx, uint64_t *val)
>          *val = v->arch.hvm_vcpu.viridian.apic_assist.raw;
>          break;
> 
> +    case VIRIDIAN_MSR_REFERENCE_TSC:
> +        if ( !(viridian_feature_mask(d) & HVMPV_reference_tsc) )
> +            return 0;
> +
> +        perfc_incr(mshv_rdmsr_tsc_msr);
> +        *val = d->arch.hvm_domain.viridian.reference_tsc.raw;
> +        break;
> +
>      case VIRIDIAN_MSR_TIME_REF_COUNT:
>      {
>          uint64_t tsc;
> @@ -452,6 +561,7 @@ static int viridian_save_domain_ctxt(struct domain
> *d, hvm_domain_context_t *h)
> 
>      ctxt.hypercall_gpa = d->arch.hvm_domain.viridian.hypercall_gpa.raw;
>      ctxt.guest_os_id   = d->arch.hvm_domain.viridian.guest_os_id.raw;
> +    ctxt.reference_tsc = d->arch.hvm_domain.viridian.reference_tsc.raw;
> 
>      return (hvm_save_entry(VIRIDIAN_DOMAIN, 0, h, &ctxt) != 0);
>  }
> @@ -460,11 +570,15 @@ static int viridian_load_domain_ctxt(struct domain
> *d, hvm_domain_context_t *h)
>  {
>      struct hvm_viridian_domain_context ctxt;
> 
> -    if ( hvm_load_entry(VIRIDIAN_DOMAIN, h, &ctxt) != 0 )
> +    if ( hvm_load_entry_zeroextend(VIRIDIAN_DOMAIN, h, &ctxt) != 0 )
>          return -EINVAL;
> 
>      d->arch.hvm_domain.viridian.hypercall_gpa.raw = ctxt.hypercall_gpa;
>      d->arch.hvm_domain.viridian.guest_os_id.raw   = ctxt.guest_os_id;
> +    d->arch.hvm_domain.viridian.reference_tsc.raw = ctxt.reference_tsc;
> +
> +    if ( d->arch.hvm_domain.viridian.reference_tsc.fields.enabled )
> +        update_reference_tsc(d, 0);
> 
>      return 0;
>  }
> diff --git a/xen/include/asm-x86/hvm/viridian.h b/xen/include/asm-
> x86/hvm/viridian.h
> index 496da33..35a22f5 100644
> --- a/xen/include/asm-x86/hvm/viridian.h
> +++ b/xen/include/asm-x86/hvm/viridian.h
> @@ -48,10 +48,35 @@ union viridian_hypercall_gpa
>      } fields;
>  };
> 
> +union viridian_reference_tsc
> +{
> +    uint64_t raw;
> +    struct
> +    {
> +        uint64_t enabled:1;
> +        uint64_t reserved_preserved:11;
> +        uint64_t pfn:48;
> +    } fields;
> +};
> +
> +/*
> + * Type defintion as in Microsoft Hypervisor Top-Level Functional
> + * Specification v4.0a, section 15.4.2.
> + */
> +typedef struct _HV_REFERENCE_TSC_PAGE
> +{
> +    uint32_t TscSequence;
> +    uint32_t Reserved1;
> +    uint64_t TscScale;
> +    int64_t  TscOffset;
> +    uint64_t Reserved2[509];
> +} HV_REFERENCE_TSC_PAGE, *PHV_REFERENCE_TSC_PAGE;
> +
>  struct viridian_domain
>  {
>      union viridian_guest_os_id guest_os_id;
>      union viridian_hypercall_gpa hypercall_gpa;
> +    union viridian_reference_tsc reference_tsc;
>  };
> 
>  int
> @@ -76,3 +101,13 @@ int
>  viridian_hypercall(struct cpu_user_regs *regs);
> 
>  #endif /* __ASM_X86_HVM_VIRIDIAN_H__ */
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * tab-width: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> diff --git a/xen/include/public/arch-x86/hvm/save.h
> b/xen/include/public/arch-x86/hvm/save.h
> index 16d85a3..006924b 100644
> --- a/xen/include/public/arch-x86/hvm/save.h
> +++ b/xen/include/public/arch-x86/hvm/save.h
> @@ -568,6 +568,7 @@ struct hvm_hw_cpu_xsave {
>  struct hvm_viridian_domain_context {
>      uint64_t hypercall_gpa;
>      uint64_t guest_os_id;
> +    uint64_t reference_tsc;
>  };
> 
>  DECLARE_HVM_SAVE_TYPE(VIRIDIAN_DOMAIN, 15, struct
> hvm_viridian_domain_context);
> @@ -616,3 +617,13 @@ struct hvm_msr {
>  #define HVM_SAVE_CODE_MAX 20
> 
>  #endif /* __XEN_PUBLIC_HVM_SAVE_X86_H__ */
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * tab-width: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> diff --git a/xen/include/public/hvm/params.h
> b/xen/include/public/hvm/params.h
> index 3c51072..a2d43bc 100644
> --- a/xen/include/public/hvm/params.h
> +++ b/xen/include/public/hvm/params.h
> @@ -92,10 +92,15 @@
>  #define _HVMPV_time_ref_count 2
>  #define HVMPV_time_ref_count  (1 << _HVMPV_time_ref_count)
> 
> +/* Enable Reference TSC Page (HV_X64_MSR_REFERENCE_TSC) */
> +#define _HVMPV_reference_tsc 3
> +#define HVMPV_reference_tsc  (1 << _HVMPV_reference_tsc)
> +
>  #define HVMPV_feature_mask \
>       (HVMPV_base_freq | \
>        HVMPV_no_freq | \
> -      HVMPV_time_ref_count)
> +      HVMPV_time_ref_count | \
> +      HVMPV_reference_tsc)
> 
>  #endif
> 
> --
> 1.7.10.4


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