Re: Oops in VMA code

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2011-06-15 at 23:54 -0700, Linus Torvalds wrote:
> On Wed, Jun 15, 2011 at 11:20 PM, Alexander Graf <agraf@suse.de> wrote:
> >
> > On 16.06.2011, at 07:59, Linus Torvalds wrote:
> >>
> >> r26 has the value 0xc00090026236bbb0, and that "90" byte in the middle
> >> there looks bogus. It's not a valid pointer any more, but if that "9"
> >> had been a zero, it would have been.
> >
> > Please see my reply to Ben here.
> 
> Your reply to Ben seems to say that 0xc00000026236bbb0 wouldn't have
> been a valid address, because you don't have that much memory.
> 
> But that's clearly not true. All the other registers have valid
> pointers in them, and the stack pointer (r1) is c000000262987cd0, for
> example. And that stack is clearly valid - if the kernel stack pointer
> was corrupted, you'd never have gotten as far as reporting the oops.
> 
> So you may have only 8GB of RAM in that machine, but if so, there's
> some empty unmapped physical space. Because clearly your RAM is _not_
> limited to being mapped to below 0xc000000200000000.

Right. It's a G5, RAM goes from 0...2G and 2G onward, with an IO hole
from 2 to 4G.

Cheers,
Ben.