Re: IA64 non-contiguous memory space bugs

[David Gibson]

On Tue, Feb 21, 2006 at 08:55:15PM -0700, David Mosberger-Tang wrote:
> I'm only following this superficially, but keep in mind that a vm-area
> MUST NEVER cross a hole.

Yes.. but it can, that's precisely the bug.

> On 2/21/06, Chen, Kenneth W <kenneth.w.chen@xxxxxxxxx> wrote:
> > David Gibson wrote on Tuesday, February 21, 2006 4:14 PM
> > > First bug (confirmed many months ago by Chris Wedgwood) - you can get
> > > weird effects if you attempt to mmap() something into one of the
> > > address space gaps.  The ia64 outer wrapper for mmap2() tries to
> > > prevent it, but doesn't do a good enough job, it's still possible
> > > indirectly with shmat() and maybe mremap().  Basic trouble is that
> > > most of the checks applied by the generic code assume that everything
> > > between 0 and TASK_SIZE is valid.
> >
> > Ha ha ha.
> >
> > On ia64, the low level tlb fault handler (vhpt_miss and nested_dtlb_miss)
> > checks that all unused address bits (between REGION_NUMBER and PGDIR_SHIFT)
> > should be all zero.  If they are not zero, it will fall into page fault
> > handler and in there, ia64 should just send SEGV instead of happily hand
> > over a page.  Buggy buggy....

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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