Re: [PATCH 2/8] KVM: X86: Store L1's TSC scaling ratio in 'struct kvm_vcpu_arch'

[Maxim Levitsky <mlevitsk@redhat.com>]

On Thu, 2021-05-06 at 10:32 +0000, ilstam@mailbox.org wrote:
> From: Ilias Stamatis <ilstam@amazon.com>
> 
> Store L1's scaling ratio in that 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@amazon.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 5 +++--
>  arch/x86/kvm/x86.c              | 4 +++-
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index cbbcee0a84f9..132e820525fb 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -705,7 +705,7 @@ 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;
> @@ -719,7 +719,8 @@ 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/x86.c b/arch/x86/kvm/x86.c
> index cebdaa1e3cf5..7bc5155ac6fd 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2119,6 +2119,7 @@ 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;
>  	}
> @@ -2145,7 +2146,7 @@ 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;
>  }
>  
> @@ -2157,6 +2158,7 @@ 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;
>  	}
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>