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

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Message-ID: <19016.41349.636663.515540@pilspetsen.it.uu.se>
Date:	Mon, 29 Jun 2009 13:12:05 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Grant Grundler <grundler@...isc-linux.org>,
	Mikael Pettersson <mikpe@...uu.se>,
	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 writes:
 > Grant Grundler wrote:
 > > On Sat, Jun 27, 2009 at 11:45:24AM +0200, Mikael Pettersson wrote:
 > > ...
 > >>   fff00000-fffffffe : pnp 00:09
 > >> 100000000-1ffffffff : System RAM
 > >> 200000000-ffffffffffffffff : RAM buffer
 > >>
 > >> With 2.6.30 things look similar, except 2.6.30 does not show the
 > >> last "200000000-ffffffffffffffff : RAM buffer" line.
 > > 
 > > BIOS e280 table didn't report that line.
 > > I expect it's created by arch/x86/kernel/e820.c:
 > > 1398         /*
 > > 1399          * Try to bump up RAM regions to reasonable boundaries to
 > > 1400          * avoid stolen RAM:
 > > 1401          */
 > > 1402         for (i = 0; i < e820.nr_map; i++) {
 > > 1403                 struct e820entry *entry = &e820_saved.map[i];
 > > 1404                 resource_size_t start, end;
 > > 1405 
 > > 1406                 if (entry->type != E820_RAM)
 > > 1407                         continue;
 > > 1408                 start = entry->addr + entry->size;
 > > 1409                 end = round_up(start, ram_alignment(start));
 > > 1410                 if (start == end)
 > > 1411                         continue;
 > > 1412                 reserve_region_with_split(&iomem_resource, start,
 > > 1413                                                   end - 1, "RAM buffer");
 > > 1414         }
 > > 
 > 
 > 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.

/Mikael
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