KVM: x86: SVM: add module param to control TSC scaling

This allows to easily simulate a CPU without this feature.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210914154825.104886-13-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 53d593016be5743e5281e9ada37f575073081b6e..1ff904653a3e541baa62d67f23c71697948afe43 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -190,6 +190,9 @@ module_param(vgif, int, 0444);
 static int lbrv = true;
 module_param(lbrv, int, 0444);
 
+static int tsc_scaling = true;
+module_param(tsc_scaling, int, 0444);
+
 /*
  * enable / disable AVIC.  Because the defaults differ for APICv
  * support between VMX and SVM we cannot use module_param_named.
@@ -470,7 +473,7 @@ static int has_svm(void)
 static void svm_hardware_disable(void)
 {
        /* Make sure we clean up behind us */
-       if (static_cpu_has(X86_FEATURE_TSCRATEMSR))
+       if (tsc_scaling)
                wrmsrl(MSR_AMD64_TSC_RATIO, TSC_RATIO_DEFAULT);
 
        cpu_svm_disable();
@@ -513,6 +516,10 @@ static int svm_hardware_enable(void)
        wrmsrl(MSR_VM_HSAVE_PA, __sme_page_pa(sd->save_area));
 
        if (static_cpu_has(X86_FEATURE_TSCRATEMSR)) {
+               /*
+                * Set the default value, even if we don't use TSC scaling
+                * to avoid having stale value in the msr
+                */
                wrmsrl(MSR_AMD64_TSC_RATIO, TSC_RATIO_DEFAULT);
                __this_cpu_write(current_tsc_ratio, TSC_RATIO_DEFAULT);
        }
@@ -980,10 +987,15 @@ static __init int svm_hardware_setup(void)
        if (boot_cpu_has(X86_FEATURE_FXSR_OPT))
                kvm_enable_efer_bits(EFER_FFXSR);
 
-       if (boot_cpu_has(X86_FEATURE_TSCRATEMSR)) {
-               kvm_has_tsc_control = true;
-               kvm_max_tsc_scaling_ratio = TSC_RATIO_MAX;
-               kvm_tsc_scaling_ratio_frac_bits = 32;
+       if (tsc_scaling) {
+               if (!boot_cpu_has(X86_FEATURE_TSCRATEMSR)) {
+                       tsc_scaling = false;
+               } else {
+                       pr_info("TSC scaling supported\n");
+                       kvm_has_tsc_control = true;
+                       kvm_max_tsc_scaling_ratio = TSC_RATIO_MAX;
+                       kvm_tsc_scaling_ratio_frac_bits = 32;
+               }
        }
 
        tsc_aux_uret_slot = kvm_add_user_return_msr(MSR_TSC_AUX);
@@ -1496,7 +1508,7 @@ static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu)
                vmsave(__sme_page_pa(sd->save_area));
        }
 
-       if (static_cpu_has(X86_FEATURE_TSCRATEMSR)) {
+       if (tsc_scaling) {
                u64 tsc_ratio = vcpu->arch.tsc_scaling_ratio;
                if (tsc_ratio != __this_cpu_read(current_tsc_ratio)) {
                        __this_cpu_write(current_tsc_ratio, tsc_ratio);