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

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Message-ID: <352e189ec40fae044206b48ca6e68d77df7dced1.camel@intel.com>
Date: Wed, 3 Dec 2025 00:50:29 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>, "dwmw2@...radead.org"
	<dwmw2@...radead.org>
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


> -#define KVM_X2APIC_API_USE_32BIT_IDS            (1ULL << 0)
> -#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK  (1ULL << 1)
> +#define KVM_X2APIC_API_USE_32BIT_IDS			(_BITULL(0))
> +#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK		(_BITULL(1))
> +#define KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST	(_BITULL(2))
> +#define KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST	(_BITULL(3))

I hate to say, but wants to ask again:

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.