linux-kernel - Re: [BUG 2.6.31-rc1] HIGHMEM64G causes hang in PCI init on 32-bit x86

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Date:	Tue, 30 Jun 2009 15:54:51 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Mikael Pettersson <mikpe@...uu.se>,
	Matthew Wilcox <matthew@....cx>,
	Grant Grundler <grundler@...isc-linux.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org
Subject: Re: [BUG 2.6.31-rc1] HIGHMEM64G causes hang in PCI init on 32-bit
 x86

Yinghai Lu wrote:
>>>
>>> Not very well tested, but it _looks_ correct, and uses Peter's trick, and 
>>> willlet the compiler notice that
>>>
>>> 	round_up(x,y)-1
>>>
>>> is the same thing as
>>>
>>> 	x | (y-1)
>>>
>>> which it _could_ have perhaps figured out before, but now it's way more 
>>> obvious.
>> how about x = 0, y = 0x100?
>>
> 
> also x=0x100000, and y=0x100?
> 

Yes, it doesn't work when x is already aligned.

	-hpa

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