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

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Message-ID: <YLtL/JPvGs2efZKO@google.com>
Date:   Sat, 5 Jun 2021 19:03:40 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Marc Zyngier <maz@...nel.org>, 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 (21/06/05 18:58), Sergey Senozhatsky wrote:
[..]
> > > +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.
> 
> No opinion. What shall we do when we fail to suspend the VM?
> VM's watchdogs will trigger and maybe panic the system after
> resume.

For the time being kvm_set_guest_paused() errors out when
!vcpu->arch.pv_time_enabled, but this probably can change
in the future (who knows?). So shall I check vcpu->arch.pv_time_enabled
in  kvm_arch_suspend_notifier()?