linux-kernel - Re: [PATCH v3 02/12] KVM: X86: Store L1's TSC scaling ratio in 'struct kvm_vcpu

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Message-ID: <05c98b5e6627ddb01bbedb08a2854d8c55bdc2d7.camel@redhat.com>
Date:   Mon, 24 May 2021 20:49:28 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Ilias Stamatis <ilstam@...zon.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com
Cc:     seanjc@...gle.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 v3 02/12] KVM: X86: Store L1's TSC scaling ratio in
 'struct kvm_vcpu_arch'

On Fri, 2021-05-21 at 11:24 +0100, Ilias Stamatis wrote:
> Store L1's scaling ratio in the kvm_vcpu_arch struct like we already do
> for L1's TSC offset. This allows for easy save/restore when we enter and
> then exit the nested guest.
> 
> Signed-off-by: Ilias Stamatis <ilstam@...zon.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 5 +++--
>  arch/x86/kvm/vmx/vmx.c          | 4 ++--
>  arch/x86/kvm/x86.c              | 6 ++++--
>  3 files changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 55efbacfc244..7dfc609eacd6 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -707,7 +707,7 @@ struct kvm_vcpu_arch {
>  	} st;
>  
>  	u64 l1_tsc_offset;
> -	u64 tsc_offset;
> +	u64 tsc_offset; /* current tsc offset */
>  	u64 last_guest_tsc;
>  	u64 last_host_tsc;
>  	u64 tsc_offset_adjustment;
> @@ -721,7 +721,8 @@ struct kvm_vcpu_arch {
>  	u32 virtual_tsc_khz;
>  	s64 ia32_tsc_adjust_msr;
>  	u64 msr_ia32_power_ctl;
> -	u64 tsc_scaling_ratio;
> +	u64 l1_tsc_scaling_ratio;
> +	u64 tsc_scaling_ratio; /* current scaling ratio */
>  
>  	atomic_t nmi_queued;  /* unprocessed asynchronous NMIs */
>  	unsigned nmi_pending; /* NMI queued after currently running handler */
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 4bceb5ca3a89..3e4dda8177bb 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7453,10 +7453,10 @@ static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc,
>  		delta_tsc = 0;
>  
>  	/* Convert to host delta tsc if tsc scaling is enabled */
> -	if (vcpu->arch.tsc_scaling_ratio != kvm_default_tsc_scaling_ratio &&
> +	if (vcpu->arch.l1_tsc_scaling_ratio != kvm_default_tsc_scaling_ratio &&
>  	    delta_tsc && u64_shl_div_u64(delta_tsc,
>  				kvm_tsc_scaling_ratio_frac_bits,
> -				vcpu->arch.tsc_scaling_ratio, &delta_tsc))
> +				vcpu->arch.l1_tsc_scaling_ratio, &delta_tsc))
>  		return -ERANGE;
>  
>  	/*
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bbc4e04e67ad..6ab95ac188a5 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;
>  		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);

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky