linux-kernel - [PATCH v3 07/12] KVM: X86: Add functions that calculate L2's TSC offset and multiplier

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Date:   Fri, 21 May 2021 11:24:44 +0100
From:   Ilias Stamatis <ilstam@...zon.com>
To:     <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <pbonzini@...hat.com>
CC:     <mlevitsk@...hat.com>, <seanjc@...gle.com>, <vkuznets@...hat.com>,
        <wanpengli@...cent.com>, <jmattson@...gle.com>, <joro@...tes.org>,
        <zamsden@...il.com>, <mtosatti@...hat.com>, <dwmw@...zon.co.uk>,
        <ilstam@...zon.com>
Subject: [PATCH v3 07/12] KVM: X86: Add functions that calculate L2's TSC offset and multiplier

When L2 is entered we need to "merge" the TSC multiplier and TSC offset
values of 01 and 12 together.

The merging is done using the following equations:
  offset_02 = ((offset_01 * mult_12) >> shift_bits) + offset_12
  mult_02 = (mult_01 * mult_12) >> shift_bits

Where shift_bits is kvm_tsc_scaling_ratio_frac_bits.

Signed-off-by: Ilias Stamatis <ilstam@...zon.com>
---
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/x86.c              | 25 +++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 0f2cf5d1240c..aaf756442ed1 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1792,6 +1792,8 @@ static inline bool kvm_is_supported_user_return_msr(u32 msr)
 
 u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc, u64 ratio);
 u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc);
+u64 kvm_calc_nested_tsc_offset(u64 l1_offset, u64 l2_offset, u64 l2_multiplier);
+u64 kvm_calc_nested_tsc_multiplier(u64 l1_multiplier, u64 l2_multiplier);
 
 unsigned long kvm_get_linear_rip(struct kvm_vcpu *vcpu);
 bool kvm_is_linear_rip(struct kvm_vcpu *vcpu, unsigned long linear_rip);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fdcb4f46a003..04abaacb9cfc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2334,6 +2334,31 @@ u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc)
 }
 EXPORT_SYMBOL_GPL(kvm_read_l1_tsc);
 
+u64 kvm_calc_nested_tsc_offset(u64 l1_offset, u64 l2_offset, u64 l2_multiplier)
+{
+	u64 nested_offset;
+
+	if (l2_multiplier == kvm_default_tsc_scaling_ratio)
+		nested_offset = l1_offset;
+	else
+		nested_offset = mul_s64_u64_shr((s64) l1_offset, l2_multiplier,
+						kvm_tsc_scaling_ratio_frac_bits);
+
+	nested_offset += l2_offset;
+	return nested_offset;
+}
+EXPORT_SYMBOL_GPL(kvm_calc_nested_tsc_offset);
+
+u64 kvm_calc_nested_tsc_multiplier(u64 l1_multiplier, u64 l2_multiplier)
+{
+	if (l2_multiplier != kvm_default_tsc_scaling_ratio)
+		return mul_u64_u64_shr(l1_multiplier, l2_multiplier,
+				       kvm_tsc_scaling_ratio_frac_bits);
+
+	return l1_multiplier;
+}
+EXPORT_SYMBOL_GPL(kvm_calc_nested_tsc_multiplier);
+
 static void kvm_vcpu_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
 {
 	vcpu->arch.l1_tsc_offset = offset;
-- 
2.17.1