linux-kernel - Re: [PATCH] KVM: x86: skip userspace IOAPIC EOI exit when Directed EOI is enabled

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Message-ID: <7F944F65-4473-440A-9A2C-235C88672E36@nutanix.com>
Date: Tue, 23 Sep 2025 03:32:31 +0000
From: Khushit Shah <khushit.shah@...anix.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Jon Kohler <jon@...anix.com>, Paolo Bonzini <pbonzini@...hat.com>,
        Thomas
 Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav
 Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: skip userspace IOAPIC EOI exit when Directed
 EOI is enabled

Thanks for the very detailed review.

> On 23 Sep 2025, at 3:21 AM, Sean Christopherson <seanjc@...gle.com> wrote:
> 
> Don't bother sending a v2, at least not yet.  I'll follow-up with various folks
> to try and figure out the least awful way to get out of this mess, and will
> probably post a v2 with a CAP and/or quirk.

I am happy to help with v2!

Reported-by: Khushit Shah <khushit.shah@...anix.com>
Tested-by: Khushit Shah <khushit.shah@...anix.com>

> On 23 Sep 2025, at 3:21 AM, Sean Christopherson <seanjc@...gle.com> wrote:
> 
> /* Request a KVM exit to inform the userspace IOAPIC. */
> if (irqchip_split(apic->vcpu->kvm)) {
> + /*
> +  * Don't exit to userspace if the guest has enabled Directed
> +  * EOI, a.k.a. Suppress EOI Broadcasts, in which the local APIC
> +  * doesn't broadcast EOIs (the the guest must EOI the target
> +  * I/O APIC(s) directly).
> +  */
> +

Nit: small typo in the comment (“the the”).