linux-kernel - Re: [PATCH v5 4/3] KVM: selftests: Add test cases for EOI suppression modes

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Message-ID: <aXt6ZEgZRGPPPtTB@google.com>
Date: Thu, 29 Jan 2026 07:19:00 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Khushit Shah <khushit.shah@...anix.com>, pbonzini@...hat.com, kai.huang@...el.com, 
	mingo@...hat.com, x86@...nel.org, bp@...en8.de, hpa@...or.com, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	dave.hansen@...ux.intel.com, tglx@...utronix.de, jon@...anix.com, 
	shaju.abraham@...anix.com
Subject: Re: [PATCH v5 4/3] KVM: selftests: Add test cases for EOI suppression modes

On Wed, Jan 28, 2026, David Woodhouse wrote:
> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> Rather than being frightened of doing the right thing for the in-kernel
> I/O APIC because "there might be bugs", 

I'm not worried about bugs per se, I'm worried about breaking existing guests.
Even if KVM is 100% perfect, changes in behavior can still break guests,
especially for a feature like this where it seems like everyone got it wrong.

And as I said before, I'm not opposed to supporting directed EOI in the in-kernel
I/O APIC, but (a) I don't want to do it in conjunction with the fixes for stable@,
and (b) I'd prefer to not bother unless there's an actual use case for doing so.
The in-kernel I/O APIC isn't being deprecated, but AFAIK it's being de-prioritized
by pretty much every VMM.  I.e. the risk vs. reward isn't there for me.