linux-kernel - Re: [PATCH] x86: fix /proc/meminfo DirectMap

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Date:	Fri, 15 Aug 2008 15:30:14 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: fix /proc/meminfo DirectMap

On Fri, 15 Aug 2008, Ingo Molnar wrote:
> * Hugh Dickins <hugh@...itas.com> wrote:
> 
> > Should we really be using level2_ident_pgt (which needs to avoid NX) 
> > for the final direct map (which wants to use NX)?  But my attempt to 
> > build up a fresh pagetable there failed miserably to boot!
> 
> hm, exactly what change have you tried? (patch?)

As soon as that kernel failed to boot, I chucked the patch away and
erased it from my mind: much better to leave such a change to the
people who are intimate with this sequence and can debug it.

It wasn't anything much, the page to use has already been set aside
for alloc_low_page, I thought it was just a matter of breaking the
association with level2_ident_pgt at the right level then letting
phys_pmd_init do its usual setup from scratch.

Maybe it didn't work because I got it slightly wrong, or maybe it
it didn't work for more subtle reasons e.g. I was then building up
the first 1GB of direct map 2MB by 2MB: if direct map is actually
used in there and falls out of TLB, I'd certainly be in trouble.

Hugh
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