Re: [PATCH MANUALSEL 5.15 3/7] x86/kvm: Preserve BSP MSR_KVM_POLL_CONTROL across suspend/resume

Paolo Bonzini
2022-04-27T16:23:51Z

> From: Wanpeng Li <wanpengli@tencent.com>
>
> [ Upstream commit 0361bdfddca20c8855ea3bdbbbc9c999912b10ff ]
>
> MSR_KVM_POLL_CONTROL is cleared on reset, thus reverting guests to
> host-side polling after suspend/resume. Non-bootstrap CPUs are
> restored correctly by the haltpoll driver because they are hot-unplugged
> during suspend and hot-plugged during resume; however, the BSP
> is not hotpluggable and remains in host-sde polling mode after
> the guest resume. The makes the guest pay for the cost of vmexits
> every time the guest enters idle.
>
> Fix it by recording BSP's haltpoll state and resuming it during guest
> resume.
>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> Message-Id: <1650267752-46796-1-git-send-email-wanpengli@tencent.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> arch/x86/kernel/kvm.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index bd7b65081eb0..d36b58e705b6 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -66,6 +66,7 @@ static DEFINE_PER_CPU_DECRYPTED(struct kvm_vcpu_pv_apf_data, apf_reason) __align
> DEFINE_PER_CPU_DECRYPTED(struct kvm_steal_time, steal_time) __aligned(64) __visible;
> static int has_steal_clock = 0;
>
> +static int has_guest_poll = 0;
> /*
> * No need for any "IO delay" on KVM
> */
> @@ -650,14 +651,26 @@ static int kvm_cpu_down_prepare(unsigned int cpu)
>
> static int kvm_suspend(void)
> {
> + u64 val = 0;
> +
> kvm_guest_cpu_offline(false);
>
> +#ifdef CONFIG_ARCH_CPUIDLE_HALTPOLL
> + if (kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL))
> + rdmsrl(MSR_KVM_POLL_CONTROL, val);
> + has_guest_poll = !(val & 1);
> +#endif
> return 0;
> }
>
> static void kvm_resume(void)
> {
> kvm_cpu_online(raw_smp_processor_id());
> +
> +#ifdef CONFIG_ARCH_CPUIDLE_HALTPOLL
> + if (kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL) && has_guest_poll)
> + wrmsrl(MSR_KVM_POLL_CONTROL, 0);
> +#endif
> }
>
> static struct syscore_ops kvm_syscore_ops = {

Acked-by: Paolo Bonzini <pbonzini@redhat.com>