linux-kernel - Re: [PATCH] [1/16] HWPOISON: Add page flag for poisoned pages

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Message-ID: <20090528075416.GY1065@one.firstfloor.org>
Date:	Thu, 28 May 2009 09:54:16 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Andi Kleen <andi@...stfloor.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	fengguang.wu@...el.com
Subject: Re: [PATCH] [1/16] HWPOISON: Add page flag for poisoned pages

On Wed, May 27, 2009 at 10:15:10PM +0100, Alan Cox wrote:
> On Wed, 27 May 2009 22:12:26 +0200 (CEST)
> Andi Kleen <andi@...stfloor.org> wrote:
> 
> > 
> > Hardware poisoned pages need special handling in the VM and shouldn't be 
> > touched again. This requires a new page flag. Define it here.
> 
> Why can't you use PG_reserved ? That already indicates the page may not
> even be present (which is effectively your situation at that point).

Right now a page must be present with PG_reserved, otherwise /dev/mem, /proc/kcore
lots of other things will explode.

> Given lots of other hardware platforms we support bus error, machine
> check, explode or do random undefined fun things when you touch pages
> that don't exist I'm not sure I see why poisoned is different here ?

It's really a special case for lots of things and mixing it up with
PG_reserved is not very useful I think. Also page flags are not 
that tight a resource anymore anyways. I think it's better to have
it separated.

However I would expect that other architectures would use poisoned
pages too for their own similar issues. It's not really a x86 specific
concept.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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