KVM: X86: Add a ratio parameter to kvm_scale_tsc()

Sometimes kvm_scale_tsc() needs to use the current scaling ratio and
other times (like when reading the TSC from user space) it needs to use
L1's scaling ratio. Have the caller specify this by passing the ratio as
a parameter.
Signed-off-by: NIlias Stamatis <ilstam@amazon.com>
Reviewed-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210526184418.28881-5-ilstam@amazon.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1795,7 +1795,7 @@ static inline bool kvm_is_supported_user_return_msr(u32 msr)
 	return kvm_find_user_return_msr(msr) >= 0;
 }
 
-u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc);
+u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc, u64 ratio);
 u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc);
 
 unsigned long kvm_get_linear_rip(struct kvm_vcpu *vcpu);

arch/x86/kvm/x86.c

@@ -2307,10 +2307,9 @@ static inline u64 __scale_tsc(u64 ratio, u64 tsc)
 	return mul_u64_u64_shr(tsc, ratio, kvm_tsc_scaling_ratio_frac_bits);
 }
 
-u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc)
+u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc, u64 ratio)
 {
 	u64 _tsc = tsc;
-	u64 ratio = vcpu->arch.tsc_scaling_ratio;
 
 	if (ratio != kvm_default_tsc_scaling_ratio)
 		_tsc = __scale_tsc(ratio, tsc);
@@ -2323,14 +2322,15 @@ static u64 kvm_compute_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 target_tsc)
 {
 	u64 tsc;
 
-	tsc = kvm_scale_tsc(vcpu, rdtsc());
+	tsc = kvm_scale_tsc(vcpu, rdtsc(), vcpu->arch.l1_tsc_scaling_ratio);
 
 	return target_tsc - tsc;
 }
 
 u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc)
 {
-	return vcpu->arch.l1_tsc_offset + kvm_scale_tsc(vcpu, host_tsc);
+	return vcpu->arch.l1_tsc_offset +
+		kvm_scale_tsc(vcpu, host_tsc, vcpu->arch.l1_tsc_scaling_ratio);
 }
 EXPORT_SYMBOL_GPL(kvm_read_l1_tsc);
 
@@ -2463,7 +2463,8 @@ static inline void adjust_tsc_offset_host(struct kvm_vcpu *vcpu, s64 adjustment)
 {
 	if (vcpu->arch.l1_tsc_scaling_ratio != kvm_default_tsc_scaling_ratio)
 		WARN_ON(adjustment < 0);
-	adjustment = kvm_scale_tsc(vcpu, (u64) adjustment);
+	adjustment = kvm_scale_tsc(vcpu, (u64) adjustment,
+				   vcpu->arch.l1_tsc_scaling_ratio);
 	adjust_tsc_offset_guest(vcpu, adjustment);
 }
 
@@ -2846,7 +2847,8 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 	/* With all the info we got, fill in the values */
 
 	if (kvm_has_tsc_control)
-		tgt_tsc_khz = kvm_scale_tsc(v, tgt_tsc_khz);
+		tgt_tsc_khz = kvm_scale_tsc(v, tgt_tsc_khz,
+					    v->arch.l1_tsc_scaling_ratio);
 
 	if (unlikely(vcpu->hw_tsc_khz != tgt_tsc_khz)) {
 		kvm_get_time_scale(NSEC_PER_SEC, tgt_tsc_khz * 1000LL,
@@ -3554,10 +3556,17 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		 * return L1's TSC value to ensure backwards-compatible
 		 * behavior for migration.
 		 */
-		u64 tsc_offset = msr_info->host_initiated ? vcpu->arch.l1_tsc_offset :
-							    vcpu->arch.tsc_offset;
+		u64 offset, ratio;
 
-		msr_info->data = kvm_scale_tsc(vcpu, rdtsc()) + tsc_offset;
+		if (msr_info->host_initiated) {
+			offset = vcpu->arch.l1_tsc_offset;
+			ratio = vcpu->arch.l1_tsc_scaling_ratio;
+		} else {
+			offset = vcpu->arch.tsc_offset;
+			ratio = vcpu->arch.tsc_scaling_ratio;
+		}
+
+		msr_info->data = kvm_scale_tsc(vcpu, rdtsc(), ratio) + offset;
 		break;
 	}
 	case MSR_MTRRcap: