linux-kernel - Re: [PATCH v4 08/17] kvm: x86: Introduce APICv pre-update hook

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Date:   Mon, 11 Nov 2019 18:08:05 -0600
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     "rkagan@...tuozzo.com" <rkagan@...tuozzo.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "graf@...zon.com" <graf@...zon.com>,
        "jschoenh@...zon.de" <jschoenh@...zon.de>,
        "karahmed@...zon.de" <karahmed@...zon.de>,
        "rimasluk@...zon.com" <rimasluk@...zon.com>,
        "Grimm, Jon" <Jon.Grimm@....com>
Subject: Re: [PATCH v4 08/17] kvm: x86: Introduce APICv pre-update hook

Roman,

On 11/4/19 4:05 PM, Roman Kagan wrote:
> On Fri, Nov 01, 2019 at 10:41:31PM +0000, Suthikulpanit, Suravee wrote:
>> AMD SVM AVIC needs to update APIC backing page mapping before changing
>> APICv mode. Introduce struct kvm_x86_ops.pre_update_apicv_exec_ctrl
>> function hook to be called prior KVM APICv update request to each vcpu.
> This again seems to mix up APIC backing page and APIC access page.
> 
> And I must be missing something obvious, but why is it necessary to
> unmap the APIC access page while AVIC is disabled?  Does keeping it
> around stand in the way when working with AVIC disabled?

I have replied to patch 07/17 with explanation.

Yes, keeping the APIC access page while disabling AVIC would cause
the SVM to not function properly.

Thanks,
Suravee

> Thanks,
> Roman.
>