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

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Date:	Mon, 29 Jun 2009 15:47:20 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
CC:	Mikael Pettersson <mikpe@...uu.se>,
	Matthew Wilcox <matthew@....cx>,
	Grant Grundler <grundler@...isc-linux.org>,
	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

H. Peter Anvin wrote:
> [Add Cc: Yinghai]
> 
> Mikael Pettersson wrote:
>>  > >  > 
>>  > >  > OK, this seems more than a wee bit strange, to say the least.  We
>>  > >  > shouldn't be reserving the entire address space; this is legitimate I/O
>>  > >  > space.
>>  > >  > 
>>  > >  > However, the reservation suddenly being improper for the root resource
>>  > >  > would definitely make things unhappy...
>>  > > 
>>  > > Reverting the two e820 changes in 2.6.31-rc1,
>>  > > 5d423ccd7ba4285f1084e91b26805e1d0ae978ed and then
>>  > > 45fbe3ee01b8e463b28c2751b5dcc0cbdc142d90,
>>  > > but keeping the iomem_resource.end cap change, makes 2.6.31-rc1
>>  > > work on my HIGHMEM64G machine.
>>  > > 
>>  > > Seems the e820 and the iomem_resource.end changes are Ok in
>>  > > isolation but break when combined.
>>  > 
>>  > With the e820 change reverted, what does /proc/iomem look like?
>>
> 
> OK.  This is starting to make sense.  I suspect this is a similar issue
> as 3b0fde0fac19c180317eb0601b3504083f4b9bf5 addresses, which is that the
> e820 code assumes -- and I don't see any exception to that in
> 45fbe3ee01b8e463b28c2751b5dcc0cbdc142d90 -- that iomem_resource covers
> the entire 64-bit address space that e820 knows.  I wonder what happens
> with "interestingly shaped" memory above 4 GB if resource_size_t is 32
> bits with that code.
> 
> In terms of address space assignment, an alternate implementation of the
> address space cap is to mark it reserved; that would unfortunately
> result in an ugly turd at the end of /proc/iomem, but that can be
> addressed if need be, too.

always enable 64bit resource for 32bit too?

YH
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