linux-kernel - Re: [PATCH 00/15] KVM: x86: Add I/O APIC kconfig, delete irq

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Message-ID: <69a46b99-83af-4913-b5ec-e993d2edde35@redhat.com>
Date: Wed, 4 Jun 2025 18:56:02 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/15] KVM: x86: Add I/O APIC kconfig, delete irq_comm.c

On 5/20/25 01:27, Sean Christopherson wrote:
> This series is prep work for the big device posted IRQs overhaul[1], in which
> Paolo suggested getting rid of arch/x86/kvm/irq_comm.c[2].  As I started
> chipping away bits of irq_comm.c to make the final code movement to irq.c as
> small as possible, I realized that (a) a rather large amount of irq_comm.c was
> actually I/O APIC code and (b) this would be a perfect opportunity to further
> isolate the I/O APIC code.
> 
> So, a bit of hacking later and voila, CONFIG_KVM_IOAPIC.  Similar to KVM's SMM
> and Xen Kconfigs, this is something we would enable in production straightaway,
> if we could magically fast-forwarded our kernel, as fully disabling I/O APIC
> emulation puts a decent chunk of guest-visible surface entirely out of reach.
> 
> Side topic, Paolo's recollection that irq_comm.c was to hold common APIs between
> x86 and Itanium was spot on.  Though when I read Paolo's mail, I parsed "ia64"
> as x86-64.  I got quite a good laugh when I eventually realized that he really
> did mean ia64 :-)

I totally did!

Looks good, other than the small comments here and there that you 
received and my "preference" for keeping kvm_setup_default_irq_routing() 
a separate function.

Thanks,

Paolo