linux-kernel - Re: [PATCH 1/5] KVM: x86: Get vmcs12 pages before checking pending interrupts

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Date:   Wed, 03 Aug 2022 22:34:48 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Mingwei Zhang <mizhang@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH 1/5] KVM: x86: Get vmcs12 pages before checking pending
 interrupts

On Wed, 2022-08-03 at 10:51 -0700, Mingwei Zhang wrote:
> On Wed, Aug 3, 2022 at 10:18 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
> > On 8/3/22 01:07, Mingwei Zhang wrote:
> > > +     /*
> > > +      * We must first get the vmcs12 pages before checking for interrupts
> > > +      * that might unblock the guest if L1 is using virtual-interrupt
> > > +      * delivery.
> > > +      */
> > > +     if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
> > > +             /*
> > > +              * If we have to ask user-space to post-copy a page,
> > > +              * then we have to keep trying to get all of the
> > > +              * VMCS12 pages until we succeed.
> > > +              */
> > > +             if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
> > > +                     kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
> > > +                     return 0;
> > > +             }
> > > +     }
> > > +
> > 
> > I think request handling (except for KVM_REQ_EVENT) could be more
> > generically moved from vcpu_enter_guest() to vcpu_run().
> 
> Yeah, sounds good to me. I can come up with an updated version. At
> least, I will remove the repeat request here.


Now it all makes sense. I do think that KVM_REQ_GET_NESTED_STATE_PAGES processing
when the vCPU is halted is indeed missing.

This reminds me that I would be *very* happy to remove the KVM_REQ_GET_NESTED_STATE_PAGES,
if by any chance there is an agreement to do so upstream.
This is yet another reason to do so to be honest.
Just my 0.2 cents of course.


Best regards,
	Maxim Levitsky



PS:
This also reminded me of an related issue:
https://lore.kernel.org/lkml/20220427173758.517087-1-pbonzini@redhat.com/T/
Any update on it?

> 
> > Paolo
> >