linux-kernel - Re: [PATCH v5 2/3] KVM: x86/ioapic: Implement support for I/O APIC version 0x20 with EOIR

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Message-ID: <77E50A19-3DFD-44E9-B4CB-5656AC1078C0@nutanix.com>
Date: Mon, 12 Jan 2026 03:22:11 +0000
From: Khushit Shah <khushit.shah@...anix.com>
To: David Woodhouse <dwmw2@...radead.org>
CC: "seanjc@...gle.com" <seanjc@...gle.com>,
        "pbonzini@...hat.com"
	<pbonzini@...hat.com>,
        "kai.huang@...el.com" <kai.huang@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        Jon
 Kohler <jon@...anix.com>,
        Shaju Abraham <shaju.abraham@...anix.com>
Subject: Re: [PATCH v5 2/3] KVM: x86/ioapic: Implement support for I/O APIC
 version 0x20 with EOIR



> On 2 Jan 2026, at 9:47 PM, David Woodhouse <dwmw2@...radead.org> wrote:
> 
> On Mon, 2025-12-29 at 15:57 +0000, Khushit Shah wrote:
>> 
>> 
>> We can't use `_respect_` here because in QUIRKED mode with in-kernel IRQCHIP:
>> 
>>   advertise = false  (version 0x11 advertised, no EOIR register)
>>   respect   = true   (legacy quirk: honor SPIV bit even if not advertised)
> 
> Oh wow, right. Since commit 0bcc3fb95b97a ("KVM: lapic: stop
> advertising DIRECTED_EOI when in-kernel IOAPIC is in use"), KVM with
> the in-kernel I/O APIC will *not* advertise the EOI suppression in the
> local APIC version register… but does actually honour the DIRECTED_EOI
> bit if the guest sets it anyway.
> 
> While with a userspace I/O APIC, KVM *will* advertise it, but not
> honour it.
> 
> Yay.
> 
> So yes, your code is the best way to do it. Sorry for the noise.


Thanks, for the review!