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: <69c98d8e34fadd14152d625956c3371e8dbb1c76.camel@infradead.org>
Date: Fri, 02 Jan 2026 16:17:53 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: Khushit Shah <khushit.shah@...anix.com>
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 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.

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