linux-kernel - Re: [PATCH v3 1/4] KVM: x86/hyperv: Calculate APIC bus frequency for hyper-v

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Date: Thu, 21 Dec 2023 19:39:01 +0200
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Isaku Yamahata <isaku.yamahata@...el.com>, kvm@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, 
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>, Vishal
 Annapurve <vannapurve@...gle.com>, Jim Mattson <jmattson@...gle.com>,
 Xiaoyao Li <xiaoyao.li@...el.com>
Cc: isaku.yamahata@...il.com
Subject: Re: [PATCH v3 1/4] KVM: x86/hyperv: Calculate APIC bus frequency
 for hyper-v

On Tue, 2023-12-19 at 00:34 -0800, Isaku Yamahata wrote:
> Remove APIC_BUS_FREUQNCY

> and calculate it based on APIC bus cycles per NS.
> APIC_BUS_FREUQNCY is used only for HV_X64_MSR_APIC_FREQUENCY.  The MSR is
> not frequently read, calculate it every time.
> 
> In order to make APIC bus frequency configurable, we need to make make two
> related constants into variables.  APIC_BUS_FREUQNCY and APIC_BUS_CYCLE_NS.
> One can be calculated from the other.

APIC_BUS_FREUQNCY is a typo.

>    APIC_BUS_CYCLES_NS = 1000 * 1000 * 1000 / APIC_BUS_FREQUENCY.
> By removing APIC_BUS_FREQUENCY, we need to track only single variable
> instead of two.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
> Changes v3:
> - Newly added according to Maxim Levistsky suggestion.
Typo: Maxim Levitsky

> ---
>  arch/x86/kvm/hyperv.c | 2 +-
>  arch/x86/kvm/lapic.h  | 1 -
>  2 files changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 238afd7335e4..a40ca2fef58c 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1687,7 +1687,7 @@ static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
>  		data = (u64)vcpu->arch.virtual_tsc_khz * 1000;
>  		break;
>  	case HV_X64_MSR_APIC_FREQUENCY:
> -		data = APIC_BUS_FREQUENCY;
> +		data = div64_u64(1000000000ULL, APIC_BUS_CYCLE_NS);
>  		break;
>  	default:
>  		kvm_pr_unimpl_rdmsr(vcpu, msr);
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index 0a0ea4b5dd8c..a20cb006b6c8 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -17,7 +17,6 @@
>  #define APIC_DEST_MASK			0x800
>  
>  #define APIC_BUS_CYCLE_NS       1
> -#define APIC_BUS_FREQUENCY      (1000000000ULL / APIC_BUS_CYCLE_NS)
>  
>  #define APIC_BROADCAST			0xFF
>  #define X2APIC_BROADCAST		0xFFFFFFFFul


Other than typos:

Reviewed-by: Maxim Levitsky <maximlevitsky@...il.com>

Best regards,
	Maxim Levitsky