linux-kernel - Re: [PATCH v2 02/10] KVM: X86: Store L1's TSC scaling ratio in 'struct kvm_vcpu

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Date:   Tue, 18 May 2021 22:52:57 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Ilias Stamatis <ilstam@...zon.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, mlevitsk@...hat.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        zamsden@...il.com, mtosatti@...hat.com, dwmw@...zon.co.uk
Subject: Re: [PATCH v2 02/10] KVM: X86: Store L1's TSC scaling ratio in
 'struct kvm_vcpu_arch'

On Wed, May 12, 2021, Ilias Stamatis wrote:
> Store L1's scaling ratio in that struct like we already do for L1's TSC

s/that struct/kvm_vcpu_arch.  Forcing the reader to look at the subject to
understand the changelog is annoying, especially when it saves all of a handful
of characters.  E.g. I often read patches without the subject in scope.

> offset. This allows for easy save/restore when we enter and then exit
> the nested guest.
> 
> Signed-off-by: Ilias Stamatis <ilstam@...zon.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---

...

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9b6bca616929..07cf5d7ece38 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2185,6 +2185,7 @@ static int set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz, bool scale)
>  
>  	/* Guest TSC same frequency as host TSC? */
>  	if (!scale) {
> +		vcpu->arch.l1_tsc_scaling_ratio = kvm_default_tsc_scaling_ratio;
>  		vcpu->arch.tsc_scaling_ratio = kvm_default_tsc_scaling_ratio;

Looks like these are always set as a pair, maybe add a helper, e.g.

static void kvm_set_l1_tsc_scaling_ratio(u64 ratio)
{
	vcpu->arch.l1_tsc_scaling_ratio = ratio;
	vcpu->arch.tsc_scaling_ratio = ratio;
}

>  		return 0;
>  	}
> @@ -2211,7 +2212,7 @@ static int set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz, bool scale)
>  		return -1;
>  	}
>  
> -	vcpu->arch.tsc_scaling_ratio = ratio;
> +	vcpu->arch.l1_tsc_scaling_ratio = vcpu->arch.tsc_scaling_ratio = ratio;
>  	return 0;
>  }
>  
> @@ -2223,6 +2224,7 @@ static int kvm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz)
>  	/* tsc_khz can be zero if TSC calibration fails */
>  	if (user_tsc_khz == 0) {
>  		/* set tsc_scaling_ratio to a safe value */
> +		vcpu->arch.l1_tsc_scaling_ratio = kvm_default_tsc_scaling_ratio;
>  		vcpu->arch.tsc_scaling_ratio = kvm_default_tsc_scaling_ratio;
>  		return -1;
>  	}
> @@ -2459,7 +2461,7 @@ static inline void adjust_tsc_offset_guest(struct kvm_vcpu *vcpu,
>  
>  static inline void adjust_tsc_offset_host(struct kvm_vcpu *vcpu, s64 adjustment)
>  {
> -	if (vcpu->arch.tsc_scaling_ratio != kvm_default_tsc_scaling_ratio)
> +	if (vcpu->arch.l1_tsc_scaling_ratio != kvm_default_tsc_scaling_ratio)
>  		WARN_ON(adjustment < 0);
>  	adjustment = kvm_scale_tsc(vcpu, (u64) adjustment);
>  	adjust_tsc_offset_guest(vcpu, adjustment);
> -- 
> 2.17.1
>