[PATCH v3 07/12] KVM: X86: Add functions that calculate L2's 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              | 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