[PATCH v2 06/10] KVM: X86: Add functions that calculate the 02 TSC offset and multiplier

[Ilias Stamatis <ilstam@amazon.com>]

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@amazon.com>
---
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/x86.c              | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4c4a3fefff57..57a25d8e8b0f 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1793,6 +1793,8 @@ static inline bool kvm_is_supported_user_return_msr(u32 msr)
 u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc);
 u64 kvm_scale_tsc_l1(struct kvm_vcpu *vcpu, u64 tsc);
 u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc);
+void kvm_set_02_tsc_offset(struct kvm_vcpu *vcpu);
+void kvm_set_02_tsc_multiplier(struct kvm_vcpu *vcpu);
 
 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 84af1af7a2cc..1db6cfc2079f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2346,6 +2346,35 @@ u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc)
 }
 EXPORT_SYMBOL_GPL(kvm_read_l1_tsc);
 
+void kvm_set_02_tsc_offset(struct kvm_vcpu *vcpu)
+{
+	u64 l2_offset = static_call(kvm_x86_get_l2_tsc_offset)(vcpu);
+	u64 l2_multiplier = static_call(kvm_x86_get_l2_tsc_multiplier)(vcpu);
+
+	if (l2_multiplier != kvm_default_tsc_scaling_ratio) {
+		vcpu->arch.tsc_offset = mul_s64_u64_shr(
+				(s64) vcpu->arch.l1_tsc_offset,
+				l2_multiplier,
+				kvm_tsc_scaling_ratio_frac_bits);
+	}
+
+	vcpu->arch.tsc_offset += l2_offset;
+}
+EXPORT_SYMBOL_GPL(kvm_set_02_tsc_offset);
+
+void kvm_set_02_tsc_multiplier(struct kvm_vcpu *vcpu)
+{
+	u64 l2_multiplier = static_call(kvm_x86_get_l2_tsc_multiplier)(vcpu);
+
+	if (l2_multiplier != kvm_default_tsc_scaling_ratio) {
+		vcpu->arch.tsc_scaling_ratio = mul_u64_u64_shr(
+				vcpu->arch.l1_tsc_scaling_ratio,
+				l2_multiplier,
+				kvm_tsc_scaling_ratio_frac_bits);
+	}
+}
+EXPORT_SYMBOL_GPL(kvm_set_02_tsc_multiplier);
+
 static void kvm_vcpu_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
 {
 	vcpu->arch.l1_tsc_offset = offset;
-- 
2.17.1