linux-kernel - Re: [PATCHv2 2/2] kvm: x86: implement KVM PM-notifier

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Date:   Sat, 05 Jun 2021 10:00:15 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Suleiman Souhlal <suleiman@...gle.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 2/2] kvm: x86: implement KVM PM-notifier

On Sat, 05 Jun 2021 03:30:42 +0100,
Sergey Senozhatsky <senozhatsky@...omium.org> wrote:
> 
> Implement PM hibernation/suspend prepare notifiers so that KVM
> can reliably set PVCLOCK_GUEST_STOPPED on VCPUs and properly
> suspend VMs.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> ---
>  arch/x86/kvm/Kconfig |  1 +
>  arch/x86/kvm/x86.c   | 33 +++++++++++++++++++++++++++++++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index fb8efb387aff..f8e6689f490b 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -43,6 +43,7 @@ config KVM
>  	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
>  	select KVM_VFIO
>  	select SRCU
> +	select HAVE_KVM_PM_NOTIFIER

if you write this as:

	select HAVE_KVM_PM_NOTIFIER if PM

...

>  	help
>  	  Support hosting fully virtualized guest machines using hardware
>  	  virtualization extensions.  You will need a fairly recent
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b594275d49b5..533d3d010a21 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -58,6 +58,7 @@
>  #include <linux/sched/isolation.h>
>  #include <linux/mem_encrypt.h>
>  #include <linux/entry-kvm.h>
> +#include <linux/suspend.h>
>  
>  #include <trace/events/kvm.h>
>  
> @@ -5615,6 +5616,38 @@ static int kvm_vm_ioctl_set_msr_filter(struct kvm *kvm, void __user *argp)
>  	return 0;
>  }
>  
> +#if defined(CONFIG_PM) && defined(CONFIG_HAVE_KVM_PM_NOTIFIER)

... you can simplify this expression to be a simple

#ifdef CONFIG_HAVE_KVM_PM_NOTIFIER

in both patches.

> +static int kvm_arch_suspend_notifier(struct kvm *kvm)
> +{
> +	struct kvm_vcpu *vcpu;
> +	int i, ret;
> +
> +	mutex_lock(&kvm->lock);
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		ret = kvm_set_guest_paused(vcpu);
> +		if (ret) {
> +			pr_err("Failed to pause guest VCPU%d: %d\n",
> +			       vcpu->vcpu_id, ret);

Is it really a good idea to fail suspend when a guest doesn't have PV
time enabled? I also wonder how useful the pr_err() is, given that it
contains no information that would help identifying which guest failed
to pause.

> +			break;
> +		}
> +	}
> +	mutex_unlock(&kvm->lock);
> +
> +	return ret ? NOTIFY_BAD : NOTIFY_DONE;
> +}
> +
> +int kvm_arch_pm_notifier(struct kvm *kvm, unsigned long state)
> +{
> +	switch (state) {
> +	case PM_HIBERNATION_PREPARE:
> +	case PM_SUSPEND_PREPARE:
> +		return kvm_arch_suspend_notifier(kvm);
> +	}
> +
> +	return NOTIFY_DONE;
> +}
> +#endif /* CONFIG_PM && CONFIG_HAVE_KVM_PM_NOTIFIER */
> +
>  long kvm_arch_vm_ioctl(struct file *filp,
>  		       unsigned int ioctl, unsigned long arg)
>  {
> -- 
> 2.32.0.rc1.229.g3e70b5a671-goog
> 
> 

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.