Re: [PATCH] kvm: x86: Update tsc multiplier on change.

[Paolo Bonzini <pbonzini@redhat.com>]

On 01/03/2016 22:36, Owen Hofmann wrote:
> vmx.c writes the TSC_MULTIPLIER field in vmx_vcpu_load, but only when a
> vcpu has migrated physical cpus. Record the last value written and
> update in vmx_vcpu_load on any change, otherwise a cpu migration must
> occur for TSC frequency scaling to take effect.
> 
> Fixes: ff2c3a1803775cc72dc6f624b59554956396b0ee
> Signed-off-by: Owen Hofmann <osh@google.com>
> ---
>  arch/x86/kvm/vmx.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index e2951b6..0ff4537 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -596,6 +596,8 @@ struct vcpu_vmx {
>  	/* Support for PML */
>  #define PML_ENTITY_NUM		512
>  	struct page *pml_pg;
> +
> +	u64 current_tsc_ratio;
>  };
>  
>  enum segment_cache_field {
> @@ -2127,14 +2129,16 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>  		rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp);
>  		vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
>  
> -		/* Setup TSC multiplier */
> -		if (cpu_has_vmx_tsc_scaling())
> -			vmcs_write64(TSC_MULTIPLIER,
> -				     vcpu->arch.tsc_scaling_ratio);
> -
>  		vmx->loaded_vmcs->cpu = cpu;
>  	}
>  
> +	/* Setup TSC multiplier */
> +	if (kvm_has_tsc_control &&
> +	    vmx->current_tsc_ratio != vcpu->arch.tsc_scaling_ratio) {
> +		vmx->current_tsc_ratio = vcpu->arch.tsc_scaling_ratio;
> +		vmcs_write64(TSC_MULTIPLIER, vmx->current_tsc_ratio);
> +	}
> +
>  	vmx_vcpu_pi_load(vcpu, cpu);
>  }
>  
> 

Applied for 4.5 and Cc: stable@vger.kernel.org.

Paolo