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SubjectRe: [BUG 2.6.31-rc1] HIGHMEM64G causes hang in PCI init on 32-bit x86
Yinghai Lu wrote:
> 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.

Mikael, can you try following patch on your system?

---
arch/x86/kernel/e820.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

Index: linux-2.6/arch/x86/kernel/e820.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/e820.c
+++ linux-2.6/arch/x86/kernel/e820.c
@@ -1400,8 +1400,8 @@ void __init e820_reserve_resources_late(
* avoid stolen RAM:
*/
for (i = 0; i < e820.nr_map; i++) {
- struct e820entry *entry = &e820_saved.map[i];
- resource_size_t start, end;
+ struct e820entry *entry = &e820.map[i];
+ u64 start, end;

if (entry->type != E820_RAM)
continue;
@@ -1409,8 +1409,10 @@ void __init e820_reserve_resources_late(
end = round_up(start, ram_alignment(start));
if (start == end)
continue;
- reserve_region_with_split(&iomem_resource, start,
- end - 1, "RAM buffer");
+ if (end != (resource_size_t)end)
+ continue;
+ reserve_region_with_split(&iomem_resource, (resource_size_t)start,
+ (resource_size_t)(end - 1), "RAM buffer");
}
}


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