linux-kernel - Re: [git pull] core, x86: make LIST

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Message-ID: <alpine.LFD.1.10.0807140758100.3305@woody.linux-foundation.org>
Date:	Mon, 14 Jul 2008 08:03:16 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Avi Kivity <avi@...ranet.com>
Subject: Re: [git pull] core, x86: make LIST_POISON less deadly

On Mon, 14 Jul 2008, Ingo Molnar wrote:
>  
> +config ILLEGAL_POINTER_VALUE
> +       hex
> +       default 0 if X86_32
> +       default 0xffffc10000000000 if X86_64

This looks like a singularly bad pointer value on x86-64.

Why not pick something that is *guaranteed* to fault? The above looks like 
any future setup that supports 41 bits of addressing and has extended the 
page tables (yes, it will happen eventually) will find that to be a 
perfectly valid address?

It's also visually confusing, since it's visually very close to a real 
kernel pointer too.

Grr.

Why not use something sane like 0xdead000000000000, which has the high bit 
set but very fundamentally isn't a valid pointer, and never will be? And 
which is a *lot* more visually obvious too!

		Linus
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