linux-kernel - [PATCH 7/8] KVM: x86: SVM: fix tsc scaling when the host doesn't support it

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Date:   Tue, 22 Mar 2022 19:24:48 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        Ingo Molnar <mingo@...hat.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 7/8] KVM: x86: SVM: fix tsc scaling when the host doesn't support it

It was decided that when TSC scaling is not supported,
the virtual MSR_AMD64_TSC_RATIO should still have the default '1.0'
value.

However in this case kvm_max_tsc_scaling_ratio is not set,
which breaks various assumptions.

Fix this by always calculating kvm_max_tsc_scaling_ratio
regardless of host support.

Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/svm.c | 4 ++--
 arch/x86/kvm/vmx/vmx.c | 7 +++----
 arch/x86/kvm/x86.c     | 4 +---
 3 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index fb31ed01086c..acf04cf4ed2a 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4763,10 +4763,10 @@ static __init int svm_hardware_setup(void)
 		} else {
 			pr_info("TSC scaling supported\n");
 			kvm_has_tsc_control = true;
-			kvm_max_tsc_scaling_ratio = SVM_TSC_RATIO_MAX;
-			kvm_tsc_scaling_ratio_frac_bits = 32;
 		}
 	}
+	kvm_max_tsc_scaling_ratio = SVM_TSC_RATIO_MAX;
+	kvm_tsc_scaling_ratio_frac_bits = 32;
 
 	tsc_aux_uret_slot = kvm_add_user_return_msr(MSR_TSC_AUX);
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 84a7500cd80c..e3a311b9ba34 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7980,12 +7980,11 @@ static __init int hardware_setup(void)
 	if (!enable_apicv)
 		vmx_x86_ops.sync_pir_to_irr = NULL;
 
-	if (cpu_has_vmx_tsc_scaling()) {
+	if (cpu_has_vmx_tsc_scaling())
 		kvm_has_tsc_control = true;
-		kvm_max_tsc_scaling_ratio = KVM_VMX_TSC_MULTIPLIER_MAX;
-		kvm_tsc_scaling_ratio_frac_bits = 48;
-	}
 
+	kvm_max_tsc_scaling_ratio = KVM_VMX_TSC_MULTIPLIER_MAX;
+	kvm_tsc_scaling_ratio_frac_bits = 48;
 	kvm_has_bus_lock_exit = cpu_has_vmx_bus_lock_detection();
 
 	set_bit(0, vmx_vpid_bitmap); /* 0 is reserved for host */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ba920e537ddf..9c27239f987f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11631,10 +11631,8 @@ int kvm_arch_hardware_setup(void *opaque)
 		u64 max = min(0x7fffffffULL,
 			      __scale_tsc(kvm_max_tsc_scaling_ratio, tsc_khz));
 		kvm_max_guest_tsc_khz = max;
-
-		kvm_default_tsc_scaling_ratio = 1ULL << kvm_tsc_scaling_ratio_frac_bits;
 	}
-
+	kvm_default_tsc_scaling_ratio = 1ULL << kvm_tsc_scaling_ratio_frac_bits;
 	kvm_init_msr_list();
 	return 0;
 }
-- 
2.26.3