linux-kernel - Re: [patch 04/14] x86/exceptions: Make IST index zero based

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Message-ID: <alpine.DEB.2.21.1904010931480.2476@nanos.tec.linutronix.de>
Date:   Mon, 1 Apr 2019 09:33:28 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [patch 04/14] x86/exceptions: Make IST index zero based

On Mon, 1 Apr 2019, Peter Zijlstra wrote:

> On Sun, Mar 31, 2019 at 11:40:24PM +0200, Thomas Gleixner wrote:
> > --- a/arch/x86/include/asm/page_64_types.h
> > +++ b/arch/x86/include/asm/page_64_types.h
> > @@ -25,11 +25,14 @@
> >  #define IRQ_STACK_ORDER (2 + KASAN_STACK_ORDER)
> >  #define IRQ_STACK_SIZE (PAGE_SIZE << IRQ_STACK_ORDER)
> >  
> > -#define DOUBLEFAULT_STACK 1
> > -#define NMI_STACK 2
> > -#define DEBUG_STACK 3
> > -#define MCE_STACK 4
> > -#define N_EXCEPTION_STACKS 4  /* hw limit: 7 */
> > +/*
> > + * The index for the tss.ist[] array. The hardware limit is 7 entries.
> > + */
> > +#define	DOUBLEFAULT_IST		0
> > +#define	NMI_IST			1
> > +#define	DEBUG_IST		2
> > +#define	MCE_IST			3
> > +#define	N_EXCEPTION_STACKS	4
> 
> Would it make sense to use an enum here?

Yes, but ASM code hates enums. We could solve that by moving it to a
different header and exposing the necessary define via asm-offsets. I'll
have a look.

Thanks,

	tglx