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

H. Peter Anvin
2009-06-29T21:53:29Z

[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.

-hpa