linux-kernel - Re: [PATCH v2 1/4] KVM: x86: move the event handling of KVM_REQ_GET_VMCS12

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Date:   Wed, 7 Sep 2022 13:35:23 +0800
From:   Yuan Yao <yuan.yao@...ux.intel.com>
To:     Mingwei Zhang <mizhang@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Oliver Upton <oupton@...gle.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v2 1/4] KVM: x86: move the event handling of
 KVM_REQ_GET_VMCS12_PAGES into a common function

On Tue, Sep 06, 2022 at 09:26:33PM -0700, Mingwei Zhang wrote:
> > > @@ -10700,6 +10706,12 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
> > >               if (kvm_cpu_has_pending_timer(vcpu))
> > >                       kvm_inject_pending_timer_irqs(vcpu);
> > >
> > > +             if (vcpu->arch.nested_get_pages_pending) {
> > > +                     r = kvm_get_nested_state_pages(vcpu);
> > > +                     if (r <= 0)
> > > +                             break;
> > > +             }
> > > +
> >
> > Will this leads to skip the get_nested_state_pages for L2 first time
> > vmentry in every L2 running iteration ? Because with above changes
> > KVM_REQ_GET_NESTED_STATE_PAGES is not set in
> > nested_vmx_enter_non_root_mode() and
> > vcpu->arch.nested_get_pages_pending is not checked in
> > vcpu_enter_guest().
> >
> Good catch. I think the diff won't work when vcpu is runnable. It only
> tries to catch the vcpu block case. Even for the vcpu block case,  the
> check of KVM_REQ_UNBLOCK is way too late. Ah, kvm_vcpu_check_block()
> is called by kvm_vcpu_block() which is called by vcpu_block(). The
> warning is triggered at the very beginning of vcpu_block(), i.e.,
> within kvm_arch_vcpu_runnable(). So, please ignore the trace in my
> previous email.
>
> In addition, my minor push back for that is
> vcpu->arch.nested_get_pages_pending seems to be another
> KVM_REQ_GET_NESTED_STATE_PAGES.

Yeah, but in concept level it's not a REQ mask lives in the
vcpu->requests which can be cached by e.g. kvm_request_pending().
It's necessary to check vcpu->arch.nested_get_pages_pending in
vcpu_enter_guest() if Sean's idea is to replace
KVM_REQ_GET_NESTED_STATE_PAGES with nested_get_pages_pending.

>
> Thanks.
> -Mingwei
>
>
> -Mingwei