Re: [BUG] hugetlb MAP_PRIVATE mapping vs /dev/zero

[David Gibson <david@gibson.dropbear.id.au>]

On Thu, Jul 01, 2004 at 08:29:18PM +0400, Oleg Nesterov wrote:
> Hello.
> 
> Hugetlbfs mmap with MAP_PRIVATE becomes MAP_SHARED
> silently, but vma->vm_flags have no VM_SHARED bit.
> I think it make sense to forbid MAP_PRIVATE in
> hugetlbfs_file_mmap() because it may confuse user
> space applications. But the real bug is that reading
> from /dev/zero into hugetlb will do:
> 
> read_zero()
> 	read_zero_pagealigned()
> 		if (vma->vm_flags & VM_SHARED)
> 			break;	// OK if MAP_PRIVATE
> 		zap_page_range();
> 		zeromap_page_range();
> 
> We can fix hugetlbfs_file_mmap() or read_zero_pagealigned()
> or both.

Err... surely we need to fix both, yes?

-- 
David Gibson			| For every complex problem there is a
david AT gibson.dropbear.id.au	| solution which is simple, neat and
				| wrong.
http://www.ozlabs.org/people/dgibson