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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v3] x86/viridian: Add Partition Reference Time enlightenment
On Mon, Oct 13, 2014 at 03:27:39PM +0100, Paul Durrant wrote:
> 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>
> ---
> v3:
> - Prevent TscSequence increment loop from being exposed to a running
> domain.
>
> v2:
> - Addressed comments from Jan:
> - Leave enlightenment out of default set and add a comment explaining
> why.
> - De-dup code surrounding adjustment of sequence number on resume.
> - Remove accidental code deletion.
>
> 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 */
Why not just something like:
p->TscSequence++;
/* Avoid both 'invalid' values */
if ( p->TscSequence == 0xFFFFFFFF || p->TscSequence == 0 )
p->TscSequence = 1;
If there's something wrong with this approach and you prefer your
'initialize' check, perhaps add some more { } since you have a
multi-statement else.
--msw
> + 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
>
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