From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: Word-at-a-time dcache name accesses
Date: Sat, 03 Mar 2012 10:47:43 -0800
Message-ID: <4F52674F.3010508@zytor.com>
References: <alpine.LFD.2.02.1203021544300.28247@i5.linux-foundation.org> <4F516811.8060800@zytor.com> <m2eht964ud.fsf@firstfloor.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>
To: Andi Kleen <andi@firstfloor.org>
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On 03/03/2012 08:12 AM, Andi Kleen wrote:
> "H. Peter Anvin" <hpa@zytor.com> writes:
> 
>> On 03/02/2012 03:46 PM, Linus Torvalds wrote:
>>>
>>> Comments?
>>>
>>
>> My biggest concern is what happens when this happens to be at the end of
>> mapped kernel memory and we overrun the page?
> 
> A long time ago (AMD K7ish) we had hardware bugs to work around in
> this area. Overlapping into some PCI hole MMIO areas could cause obscure
> hangs.  That is why I was always careful to not do that in any x86
> library code.
> 

We still map too much, though.  That's a separate problems which should
be fixed in its own right, though.

	-hpa