Re: [PATCH v6 02/36] KVM: x86: Improve accuracy of KVM clock when TSC scaling is in force

[Sean Christopherson <seanjc@google.com>]

On Fri, Jul 03, 2026, David Woodhouse wrote:
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index f14009f25a3b..b2446c04a076 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -950,7 +950,7 @@ struct kvm_vcpu_arch {
>  	gpa_t time;
>  	s8  pvclock_tsc_shift;
>  	u32 pvclock_tsc_mul;
> -	unsigned int hw_tsc_khz;
> +	u64 hw_tsc_hz;
>  	struct gfn_to_pfn_cache pv_time;
>  	/* set guest stopped flag in pvclock flags field */
>  	bool pvclock_set_guest_stopped_request;
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index e69156b54cff..621d950ec692 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -2131,7 +2131,7 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
>  				*ecx = vcpu->arch.pvclock_tsc_mul;
>  				*edx = vcpu->arch.pvclock_tsc_shift;
>  			} else if (index == 2) {
> -				*eax = vcpu->arch.hw_tsc_khz;
> +				*eax = div_u64(vcpu->arch.hw_tsc_hz, 1000);

Kinda silly, but s/1000/HZ_PER_KHZ.

>  			}
>  		}
>  	} else {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0550359ed798..dbcff49cd561 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3314,7 +3314,8 @@ static void kvm_setup_guest_pvclock(struct pvclock_vcpu_time_info *ref_hv_clock,
>  int kvm_guest_time_update(struct kvm_vcpu *v)
>  {
>  	struct pvclock_vcpu_time_info hv_clock = {};
> -	unsigned long flags, tgt_tsc_khz;
> +	unsigned long flags;
> +	u64 tgt_tsc_hz;
>  	unsigned seq;
>  	struct kvm_vcpu_arch *vcpu = &v->arch;
>  	struct kvm_arch *ka = &v->kvm->arch;
> @@ -3340,8 +3341,8 @@ int kvm_guest_time_update(struct kvm_vcpu *v)
>  
>  	/* Keep irq disabled to prevent changes to the clock */
>  	local_irq_save(flags);
> -	tgt_tsc_khz = get_cpu_tsc_khz();
> -	if (unlikely(tgt_tsc_khz == 0)) {
> +	tgt_tsc_hz = (u64)get_cpu_tsc_khz() * 1000;

Here too.