linux-kernel - Re: [PATCH] [4/7] Don't use large pages to map the first 2/4MB of memory

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Message-ID: <47D76C72.2080603@cosmosbay.com>
Date:	Wed, 12 Mar 2008 06:38:58 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	andreas.herrmann3@....com, tglx@...utronix.de, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [4/7] Don't use large pages to map the first 2/4MB of
 memory

Andi Kleen a écrit :
> Intel recommends to not use large pages for the first 1MB 
> of the physical memory because there are fixed size MTRRs there
> which cause splitups in the TLBs.
> 
> On AMD doing so is also a good idea.
> 
> The implementation is a little different between 32bit and 64bit.
> On 32bit I just taught the initial page table set up about this
> because it was very simple to do. This also has the advantage
> that the risk of a prefetch ever seeing the page even
> if it only exists for a short time is minimized.
> 
> On 64bit that is not quite possible, so use set_memory_4k() a little
> later (in check_bugs) instead.
> 
> Signed-off-by: Andi Kleen <ak@...e.de>
> 
> ---
>  arch/x86/kernel/bugs_64.c |   12 ++++++++++++
>  arch/x86/mm/init_32.c     |    6 +++++-
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 

Should we then change CONFIG_PHYSICAL_START from 0x100000 to 0x400000 ?

Thank you
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