linux-kernel - Re: [PATCH 4/8] KVM: x86: interrupt based APF page-ready event delivery

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Date:   Wed, 13 May 2020 14:46:41 -0400
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        Gavin Shan <gshan@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] KVM: x86: interrupt based APF page-ready event
 delivery

On Wed, May 13, 2020 at 04:23:55PM +0200, Vitaly Kuznetsov wrote:

[..]
> >> Also,
> >> kdump kernel may not even support APF so it will get very confused when
> >> APF events get delivered.
> >
> > New kernel can just ignore these events if it does not support async
> > pf? 
> >
> > This is somewhat similar to devices still doing interrupts in new
> > kernel. And solution for that seemed to be doing a "reset" of devices
> > in new kernel. We probably need similar logic where in new kernel
> > we simply disable "async pf" so that we don't get new notifications.
> 
> Right and that's what we're doing - just disabling new notifications.

Nice.

So why there is a need to deliver "page ready" notifications
to guest after guest has disabled async pf. Atleast kdump does not
seem to need it. It will boot into second kernel anyway, irrespective
of the fact whether it receives page ready or not.

Thanks
Vivek