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.  For consistency, do the same for VMX.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220322172449.235575-8-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: Maxim Levitsky

arch/x86/kvm/svm/svm.c

@@ -4752,10 +4752,10 @@ 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);
 

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 */

arch/x86/kvm/x86.c

@@ -11602,10 +11602,8 @@ 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;
 }