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Date: Thu, 1 Sep 2016 17:26:15 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: peterhornyack@...gle.com, rkrcmar@...hat.com, den@...nvz.org,
rkagan@...tuozzo.com, Andrey Smetanin <asmetanin@...tuozzo.com>
Subject: [PATCH 4/4] KVM: x86: Hyper-V tsc page setup
Lately tsc page was implemented but filled with empty
values. This patch setup tsc page scale and offset based
on vcpu tsc, tsc_khz and HV_X64_MSR_TIME_REF_COUNT value.
The valid tsc page drops HV_X64_MSR_TIME_REF_COUNT msr
reads count to zero which potentially improves performance.
Signed-off-by: Andrey Smetanin <asmetanin@...tuozzo.com>
Reviewed-by: Peter Hornyack <peterhornyack@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>
CC: Radim Krčmář <rkrcmar@...hat.com>
CC: Roman Kagan <rkagan@...tuozzo.com>
CC: Denis V. Lunev <den@...nvz.org>
[Computation of TSC page parameters rewritten to use the Linux timekeeper
parameters. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
arch/x86/kvm/hyperv.c | 141 ++++++++++++++++++++++++++++++++++++++++++++------
arch/x86/kvm/hyperv.h | 3 ++
arch/x86/kvm/x86.c | 8 +--
3 files changed, 133 insertions(+), 19 deletions(-)
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index ed5b77f39ffb..e089d1f52dc0 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -756,6 +756,129 @@ static int kvm_hv_msr_set_crash_data(struct kvm_vcpu *vcpu,
return 0;
}
+/*
+ * The kvmclock and Hyper-V TSC page use similar formulas. Because the KVM
+ * one is more precise, it is a little more complex. However, converting
+ * between them is possible:
+ *
+ * kvmclock formula:
+ * nsec = (ticks - tsc_timestamp) * tsc_to_system_mul * 2^(tsc_shift-32)
+ * + system_time
+ *
+ * Hyper-V formula:
+ * nsec/100 = ticks * scale / 2^64 + offset
+ *
+ * When tsc_timestamp = system_time = 0, offset is zero in the Hyper-V formula.
+ * By dividing the kvmclock formula by 100 and equating what's left we get:
+ * ticks * scale / 2^64 = ticks * tsc_to_system_mul * 2^(tsc_shift-32) / 100
+ * scale / 2^64 = tsc_to_system_mul * 2^(tsc_shift-32) / 100
+ * scale = tsc_to_system_mul * 2^(32+tsc_shift) / 100
+ *
+ * Now expand the kvmclock formula and divide by 100:
+ * nsec = ticks * tsc_to_system_mul * 2^(tsc_shift-32)
+ * - tsc_timestamp * tsc_to_system_mul * 2^(tsc_shift-32)
+ * + system_time
+ * nsec/100 = ticks * tsc_to_system_mul * 2^(tsc_shift-32) / 100
+ * - tsc_timestamp * tsc_to_system_mul * 2^(tsc_shift-32) / 100
+ * + system_time / 100
+ *
+ * Replace tsc_to_system_mul * 2^(tsc_shift-32) / 100 by scale / 2^64:
+ * nsec/100 = ticks * scale / 2^64
+ * - tsc_timestamp * scale / 2^64
+ * + system_time / 100
+ *
+ * Equate with the Hyper-V formula so that ticks * scale / 2^64 cancels out:
+ * offset = system_time / 100 - tsc_timestamp * scale / 2^64
+ *
+ * These two equivalencies are implemented in this function.
+ */
+static bool compute_tsc_page_parameters(struct pvclock_vcpu_time_info *hv_clock,
+ HV_REFERENCE_TSC_PAGE *tsc_ref)
+{
+ u64 max_mul;
+
+ if (!(hv_clock->flags & PVCLOCK_TSC_STABLE_BIT))
+ return false;
+
+ /*
+ * check if scale would overflow, if so we use the time ref counter
+ * tsc_to_system_mul * 2^(tsc_shift+32) / 100 >= 2^64
+ * tsc_to_system_mul / 100 >= 2^(32-tsc_shift)
+ * tsc_to_system_mul >= 100 * 2^(32-tsc_shift)
+ */
+ max_mul = 100ull << (32 - hv_clock->tsc_shift);
+ if (hv_clock->tsc_to_system_mul >= max_mul)
+ return false;
+
+ /*
+ * Otherwise compute the scale and offset according to the formulas
+ * derived above.
+ */
+ tsc_ref->tsc_scale =
+ mul_u64_u32_div(1ULL << (32 + hv_clock->tsc_shift),
+ hv_clock->tsc_to_system_mul,
+ 100);
+
+ tsc_ref->tsc_offset = hv_clock->system_time;
+ do_div(tsc_ref->tsc_offset, 100);
+ tsc_ref->tsc_offset -=
+ mul_u64_u64_shr(hv_clock->tsc_timestamp, tsc_ref->tsc_scale, 64);
+ return true;
+}
+
+void kvm_hv_setup_tsc_page(struct kvm *kvm,
+ struct pvclock_vcpu_time_info *hv_clock)
+{
+ struct kvm_hv *hv = &kvm->arch.hyperv;
+ HV_REFERENCE_TSC_PAGE tsc_ref = { 0 };
+ u32 tsc_seq;
+ u64 gfn;
+
+ BUILD_BUG_ON(sizeof(tsc_seq) != sizeof(tsc_ref.tsc_sequence));
+ BUILD_BUG_ON(offsetof(HV_REFERENCE_TSC_PAGE, tsc_sequence) != 0);
+
+ if (!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE))
+ return;
+
+ gfn = hv->hv_tsc_page >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;
+ /*
+ * Because the TSC parameters only vary when there is a
+ * change in the master clock, do not bother with caching.
+ */
+ if (unlikely(kvm_read_guest(kvm, gfn_to_gpa(gfn),
+ &tsc_seq, sizeof(tsc_seq))))
+ return;
+
+ /*
+ * While we're computing and writing the parameters, force the
+ * guest to use the time reference count MSR.
+ */
+ if (kvm_write_guest(kvm, gfn_to_gpa(gfn),
+ &tsc_ref, sizeof(tsc_ref.tsc_sequence)))
+ return;
+
+ if (!compute_tsc_page_parameters(hv_clock, &tsc_ref))
+ return;
+
+ /* Ensure sequence is zero before writing the rest of the struct. */
+ smp_wmb();
+ if (kvm_write_guest(kvm, gfn_to_gpa(gfn), &tsc_ref, sizeof(tsc_ref)))
+ return;
+
+ /*
+ * Now switch to the TSC page mechanism by writing the sequence.
+ */
+ if (tsc_seq == 0xFFFFFFFF || tsc_seq == 0)
+ tsc_seq = 1;
+ else
+ tsc_seq++;
+
+ /* Write the struct entirely before the non-zero sequence. */
+ smp_wmb();
+
+ kvm_write_guest(kvm, gfn_to_gpa(gfn), &tsc_seq, sizeof(tsc_seq));
+}
+
static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
bool host)
{
@@ -793,23 +916,11 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
mark_page_dirty(kvm, gfn);
break;
}
- case HV_X64_MSR_REFERENCE_TSC: {
- u64 gfn;
- HV_REFERENCE_TSC_PAGE tsc_ref;
-
- memset(&tsc_ref, 0, sizeof(tsc_ref));
+ case HV_X64_MSR_REFERENCE_TSC:
hv->hv_tsc_page = data;
- if (!(data & HV_X64_MSR_TSC_REFERENCE_ENABLE))
- break;
- gfn = data >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;
- if (kvm_write_guest(
- kvm,
- gfn << HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT,
- &tsc_ref, sizeof(tsc_ref)))
- return 1;
- mark_page_dirty(kvm, gfn);
+ if (hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE)
+ kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
break;
- }
case HV_X64_MSR_CRASH_P0 ... HV_X64_MSR_CRASH_P4:
return kvm_hv_msr_set_crash_data(vcpu,
msr - HV_X64_MSR_CRASH_P0,
diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
index 60eccd4bd1d3..cd1119538add 100644
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -84,4 +84,7 @@ static inline bool kvm_hv_has_stimer_pending(struct kvm_vcpu *vcpu)
void kvm_hv_process_stimers(struct kvm_vcpu *vcpu);
+void kvm_hv_setup_tsc_page(struct kvm *kvm,
+ struct pvclock_vcpu_time_info *hv_clock);
+
#endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2edcfa054cbe..2e792bf80912 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1881,10 +1881,10 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
vcpu->hv_clock.flags = pvclock_flags;
- if (!vcpu->pv_time_enabled)
- return 0;
-
- kvm_setup_pvclock_page(v);
+ if (vcpu->pv_time_enabled)
+ kvm_setup_pvclock_page(v);
+ if (v == kvm_get_vcpu(v->kvm, 0))
+ kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
return 0;
}
--
1.8.3.1
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