linux-kernel - Re: [PATCH v3] KVM: x86: Add x2APIC "features" to control EOI broadcast suppression

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Message-ID: <69a5cd834b3196606b805f384353e3d9fc839981.camel@infradead.org>
Date: Wed, 03 Dec 2025 01:14:13 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: "Huang, Kai" <kai.huang@...el.com>, "seanjc@...gle.com"
 <seanjc@...gle.com>
Cc: "shaju.abraham@...anix.com" <shaju.abraham@...anix.com>, 
 "khushit.shah@...anix.com" <khushit.shah@...anix.com>, "x86@...nel.org"
 <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>, "stable@...r.kernel.org"
 <stable@...r.kernel.org>,  "hpa@...or.com" <hpa@...or.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
 "mingo@...hat.com" <mingo@...hat.com>, "dave.hansen@...ux.intel.com"
 <dave.hansen@...ux.intel.com>,  "pbonzini@...hat.com"
 <pbonzini@...hat.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "Kohler, Jon" <jon@...anix.com>, "tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH v3] KVM: x86: Add x2APIC "features" to control EOI
 broadcast suppression

On Wed, 2025-12-03 at 00:50 +0000, Huang, Kai wrote:
> 
> Since it's uAPI, are we expecting the two flags to have impact on in-kernel
> ioapic?
> 
> I think there should no harm to make the two also apply to in-kernel ioapic.
> 
> E.g., for now we can reject KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST flag for
> in-kernel ioapic.  In the future, we might add EOI register support to in-kernel
> ioapic and report supporting suppress EOI broadcast, then we can in-kernel
> ioapic to honor these two flags too.

The simplest option is probably to fix the in-kernel I/O APIC at the
same time, bumping the version to 0x20 and adding support for the EOI
register in the KVM_SUPPRESS_EOI_ENABLED case.

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