linux-kernel - Re: [PATCH] x86/kvmclock: Stop kvmclocks for hibernate restore

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Message-ID: <6bde62aa-2c57-13bb-0380-93462a51f9cf@redhat.com>
Date:   Fri, 26 Mar 2021 13:14:03 -0400
From:   Lenny Szubowicz <lszubowi@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     pbonzini@...hat.com, seanjc@...gle.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/kvmclock: Stop kvmclocks for hibernate restore

On 3/26/21 9:01 AM, Vitaly Kuznetsov wrote:
> Vitaly Kuznetsov <vkuznets@...hat.com> writes:
> 
> ..
> 
>> (this is with your v2 included). There's nothing about CPU0 for
>> e.g. async PF + timestamps are really interesting. Seems we have issues
>> to fix) I'm playing with it right now.
> 
> What if we do the following (instead of your patch):
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 78bb0fae3982..c32392d6329d 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -26,6 +26,7 @@
>   #include <linux/kprobes.h>
>   #include <linux/nmi.h>
>   #include <linux/swait.h>
> +#include <linux/syscore_ops.h>
>   #include <asm/timer.h>
>   #include <asm/cpu.h>
>   #include <asm/traps.h>
> @@ -598,17 +599,21 @@ static void kvm_guest_cpu_offline(void)
>   
>   static int kvm_cpu_online(unsigned int cpu)
>   {
> -	local_irq_disable();
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
>   	kvm_guest_cpu_init();
> -	local_irq_enable();
> +	local_irq_restore(flags);
>   	return 0;
>   }
>   
>   static int kvm_cpu_down_prepare(unsigned int cpu)
>   {
> -	local_irq_disable();
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
>   	kvm_guest_cpu_offline();
> -	local_irq_enable();
> +	local_irq_restore(flags);
>   	return 0;
>   }
>   #endif
> @@ -639,6 +644,23 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask,
>   	native_flush_tlb_others(flushmask, info);
>   }
>   
> +static int kvm_suspend(void)
> +{
> +	kvm_guest_cpu_offline();
> +
> +	return 0;
> +}
> +
> +static void kvm_resume(void)
> +{
> +	kvm_cpu_online(raw_smp_processor_id());
> +}
> +
> +static struct syscore_ops kvm_syscore_ops = {
> +	.suspend	= kvm_suspend,
> +	.resume		= kvm_resume,
> +};
> +
>   static void __init kvm_guest_init(void)
>   {
>   	int i;
> @@ -681,6 +703,8 @@ static void __init kvm_guest_init(void)
>   	kvm_guest_cpu_init();
>   #endif
>   
> +	register_syscore_ops(&kvm_syscore_ops);
> +
>   	/*
>   	 * Hard lockup detection is enabled by default. Disable it, as guests
>   	 * can get false positives too easily, for example if the host is
> 

Yes, I do like using register_syscore_ops for this. I will base my V3 on this. -Lenny.