linux-kernel - Re: Word-at-a-time dcache name accesses

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Date:	Sat, 03 Mar 2012 10:47:43 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: Word-at-a-time dcache name accesses

On 03/03/2012 08:12 AM, Andi Kleen wrote:
> "H. Peter Anvin" <hpa@...or.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


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