From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?UTF-8?Q?Mika_Penttil=c3=a4?= <mika.penttila@nextfour.com>
Subject: Re: [PATCH 1/5] kvm/x86: fix inversed check for async_pf MSR
Date: Fri, 2 Dec 2016 17:24:55 +0200
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> > > > > --- a/arch/x86/kvm/x86.c
> > > > > +++ b/arch/x86/kvm/x86.c
> > > > > @@ -8402,7 +8402,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
> > > > > bool kvm_arch_can_inject_async_page_present(struct kvm_vcpu *vcpu)
> > > > > {
> > > > > 	if (!(vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED))
> > > > > -		return true;
> > > > > +		return false;
> > > > > 
> > > > > 
> > > > Why do you make this change?
> > 
> > > Because the code does the opposite of what it's meant to do.
> > 
> > It could have a better name but returning "true" is right. See below.
> > 
> >  > > I think kvm_arch_async_page_present() is not
> > > > ever called now and neither kvm_del_async_pf_gfn(vcpu, work->arch.gfn);
> > > I wonder how you came to such a conclusion?  I certainly see them called
> > > on my test machine (you need to have the guest memory swapped out for
> > > that, that can be forced e.g. using a memory cgroup).
> > if !KVM_ASYNC_PF_ENABLED then kvm_check_async_pf_completion(), it's only call site, never calls it.

> How's that?  I don't see any check for it in
> kvm_check_async_pf_completion().  Moreover, that's exactly where it does
> that check.

void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
{
        struct kvm_async_pf *work;

        while (!list_empty_careful(&vcpu->async_pf.done) &&
              kvm_arch_can_inject_async_page_present(vcpu)) {
                spin_lock(&vcpu->async_pf.lock);
  

and you made kvm_arch_can_inject_async_page_present(vcpu) return false if !KVM_ASYNC_PF_ENABLED (i.e. not enabled)


> > Maybe you had KVM_ASYNC_PF_ENABLED?

> Of course I did.  Not sure I get what you mean...

I mean if the guest support for async pf is not enabled you maybe broke that?

--Mika