linux-kernel - Re: [RFC v2 6/9] x86/apic: Introduce Remote Action Request Operations

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Message-ID: <75fc457e8c4cf40b83743bd590f03ca22acd9e8e.camel@surriel.com>
Date: Tue, 03 Jun 2025 20:11:26 -0400
From: Rik van Riel <riel@...riel.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org, 
	kernel-team@...a.com, dave.hansen@...ux.intel.com, luto@...nel.org, 
	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	hpa@...or.com, nadav.amit@...il.com, Rik van Riel <riel@...com>, Yu-cheng
 Yu	 <yu-cheng.yu@...el.com>
Subject: Re: [RFC v2 6/9] x86/apic: Introduce Remote Action Request
 Operations

On Tue, 2025-05-20 at 11:16 +0200, Ingo Molnar wrote:
> 
> * Rik van Riel <riel@...riel.com> wrote:
> 
> > diff --git a/arch/x86/include/asm/irq_vectors.h
> > b/arch/x86/include/asm/irq_vectors.h
> > index 47051871b436..c417b0015304 100644
> > --- a/arch/x86/include/asm/irq_vectors.h
> > +++ b/arch/x86/include/asm/irq_vectors.h
> > @@ -103,6 +103,11 @@
> >   */
> >  #define POSTED_MSI_NOTIFICATION_VECTOR	0xeb
> >  
> > +/*
> > + * RAR (remote action request) TLB flush
> > + */
> > +#define RAR_VECTOR			0xe0
> > +
> >  #define NR_VECTORS			 256
> 
> This subtly breaks x86 IRQ vector allocation AFAICS.
> 
> Right now device IRQ vectors are allocated from 0x81 to 
> FIRST_SYSTEM_VECTOR (POSTED_MSI_NOTIFICATION_VECTOR) or 0xeb.
> 
> But RAR_VECTOR is within that range, the the IRQ allocator will
> overlap 
> it and result in what I guess will be misbehaving RAR code and 
> misbehaving device IRQ handling once it hands out 0xeb as well.

Sure enough! After fixing this issue, the nearly instant
segfaults for programs using RAR are no longer happening.

I'll let it run tests overnight, and will hopefully be able
to post a reliable v3 tomorrow.

Thank you!

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