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

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Message-ID: <09cec4fd-2d79-4925-bb2b-7814032fdda3@intel.com>
Date: Thu, 21 Dec 2023 13:26:58 +0800
From: Xiaoyao Li <xiaoyao.li@...el.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>,
 Maxim Levitsky <mlevitsk@...hat.com>
Cc: isaku.yamahata@...il.com
Subject: Re: [PATCH v3 1/4] KVM: x86/hyperv: Calculate APIC bus frequency for
 hyper-v

On 12/19/2023 4:34 PM, 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

two 'make', please drop one.

> related constants into variables.  APIC_BUS_FREUQNCY and APIC_BUS_CYCLE_NS.
> One can be calculated from the other.
>     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.
> ---
>   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