linux-kernel - Re: [PATCH v4 13/17] kvm: i8254: Deactivate APICv when using in-kernel PIT re-injection mode.

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Message-ID: <ac4313a6-df96-2223-bed3-33c3a8555c98@redhat.com>
Date:   Tue, 5 Nov 2019 23:47:47 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "rkagan@...tuozzo.com" <rkagan@...tuozzo.com>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "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 13/17] kvm: i8254: Deactivate APICv when using
 in-kernel PIT re-injection mode.

On 05/11/19 00:17, Roman Kagan wrote:
>> This is not too nice for Intel which does support (through the EOI exit
>> mask) APICv even if PIT reinjection active.
> Hmm, it's tempting to just make svm_load_eoi_exitmap() disable AVIC when
> given a non-empty eoi_exit_bitmap, and enable it back on a clear
> eoi_exit_bitmap.  This may remove the need to add special treatment to
> PIT etc.

That is a very nice idea---we can make that a single disable reason,
like APICV_DEACTIVATE_REASON_EOI, and Intel can simply never use it.

Paolo