linux-kernel - Re: [PATCH v3 15/16] kvm: x86: ioapic: Lazy update IOAPIC EOI

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Message-ID: <46754b8f-ed86-f622-0f9a-0fc1ffb2cb0c@redhat.com>
Date:   Fri, 1 Nov 2019 00:09:03 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "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 v3 15/16] kvm: x86: ioapic: Lazy update IOAPIC EOI

On 31/10/19 16:17, Suthikulpanit, Suravee wrote:
> What if we change kvm->arch.apicv_state to kvm->arch.apicv_disable_mask 
> and have each bit representing the reason for deactivating APICv.
> 
> For example:
>      #define APICV_DISABLE_MASK_IRQWIN        0
>      #define APICV_DISABLE_MASK_HYPERV        1
>      #define APICV_DISABLE_MASK_PIT_REINJ     2
>      #define APICV_DISABLE_MASK_NESTED        3
> 
> In this case, we activate APICv only if kvm->arch.apicv_disable_mask == 
> 0. This way, we can find out why APICv is deactivated on a particular VM 
> at a particular point in time.

Yes, that also works for me if it makes for an easier implementation.

Paolo