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

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Date:   Mon, 1 Apr 2019 09:30:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
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 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?