Re: [PATCH MANUALSEL 5.10 1/4] x86/kvm: Preserve BSP MSR_KVM_POLL_CONTROL across suspend/resume

From: Paolo Bonzini <pbonzini@redhat.com>
To: Sasha Levin <sashal@kernel.org>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Wanpeng Li <wanpengli@tencent.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	dave.hansen@linux.intel.com, x86@kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH MANUALSEL 5.10 1/4] x86/kvm: Preserve BSP MSR_KVM_POLL_CONTROL across suspend/resume
Date: Wed, 27 Apr 2022 18:19:03 +0200	[thread overview]
Message-ID: <bfe99275-a15e-306b-d628-d68754e52c2d@redhat.com> (raw)
In-Reply-To: <20220427155435.19554-1-sashal@kernel.org>

On 4/27/22 17:54, Sasha Levin wrote:
> 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 18e952fed021..6c3d38b5a8ad 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
>    */
> @@ -624,14 +625,26 @@ 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>