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

Paolo Bonzini
2016-03-02T09:38:46Z

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