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This means that the guest value is loaded on VMRUN and >>> the host value is restored from the host save area on #VMEXIT. >>> >>> Since the value is restored on #VMEXIT, the KVM user return MSR support >>> for TSC_AUX can be replaced by populating the host save area with current >>> host value of TSC_AUX. This replaces two WRMSR instructions with a single >>> RDMSR instruction. >>> >>> Signed-off-by: Tom Lendacky >>> --- >>> arch/x86/kvm/svm/sev.c | 14 +++++++++++++- >>> arch/x86/kvm/svm/svm.c | 26 ++++++++++++++++---------- >>> arch/x86/kvm/svm/svm.h | 4 +++- >>> 3 files changed, 32 insertions(+), 12 deletions(-) >>> >>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c >>> index 565c9de87c6d..1bbaae2fed96 100644 >>> --- a/arch/x86/kvm/svm/sev.c >>> +++ b/arch/x86/kvm/svm/sev.c >>> @@ -2969,6 +2969,7 @@ static void sev_es_init_vmcb_after_set_cpuid(struct vcpu_svm *svm) >>> if (boot_cpu_has(X86_FEATURE_V_TSC_AUX) && >>> (guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) || >>> guest_cpuid_has(vcpu, X86_FEATURE_RDPID))) { >>> + svm->v_tsc_aux = true; >>> set_msr_interception(vcpu, svm->msrpm, MSR_TSC_AUX, 1, 1); >>> if (guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP)) >>> svm_clr_intercept(svm, INTERCEPT_RDTSCP); >>> @@ -3071,8 +3072,10 @@ void sev_es_vcpu_reset(struct vcpu_svm *svm) >>> sev_enc_bit)); >>> } >>> >>> -void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa) >>> +void sev_es_prepare_switch_to_guest(struct vcpu_svm *svm, struct sev_es_save_area *hostsa) >>> { >>> + u32 msr_hi; >>> + >>> /* >>> * All host state for SEV-ES guests is categorized into three swap types >>> * based on how it is handled by hardware during a world switch: >>> @@ -3109,6 +3112,15 @@ void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa) >>> hostsa->dr2_addr_mask = amd_get_dr_addr_mask(2); >>> hostsa->dr3_addr_mask = amd_get_dr_addr_mask(3); >>> } >>> + >>> + /* >>> + * If TSC_AUX virtualization is enabled, MSR_TSC_AUX is loaded but NOT >>> + * saved by the CPU (Type-B). If TSC_AUX is not virtualized, the user >>> + * return MSR support takes care of restoring MSR_TSC_AUX. This >>> + * exchanges two WRMSRs for one RDMSR. >>> + */ >>> + if (svm->v_tsc_aux) >>> + rdmsr(MSR_TSC_AUX, hostsa->tsc_aux, msr_hi); >> >> IIUC, when V_TSC_AUX is supported, SEV-ES guests context switch MSR_TSC_AUX >> regardless of what has been exposed to the guest. So rather than condition the >> hostsa->tsc_aux update on guest CPUID, just do it if V_TSC_AUX is supported. >> >> And then to avoid the RDMSR, which is presumably the motivation for checking >> guest CPUID, grab the host value from user return framework. The host values >> are per-CPU, but constant after boot, so the only requirement is that KVM sets >> up MSR_TSC_AUX in the user return framework. > > Actually, duh. The save area is also per-CPU, so just fill hostsa->tsc_aux in > svm_hardware_setup() and then sev_es_prepare_switch_to_guest() never has to do > anything. Ah, right, because Linux never changes TSC_AUX post boot. Much simpler. I'll rework based on the comments and send a v2 series. Thanks, Tom