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

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Date:   Tue, 6 Sep 2022 21:26:33 -0700
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Yuan Yao <yuan.yao@...ux.intel.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

> > @@ -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.

Thanks.
-Mingwei


-Mingwei