Re: FIXMAP-related change to mm/memory.c

[Linus Torvalds]

On Thu, 12 Jun 2003, David Mosberger wrote:
>
> Is it possible to constrain the FIXADDR range on x86/x86-64
> (FIXADDR_START-FIXADDR_TOP) such that the entire range is read-only by
> user-level?  If so, we could simplify the permission test like this:

Well, you could replace the uses of FIXADDR_START/FIXADDR_TOP with 
something like FIXADDR_USER_START/FIXADDR_USER_TOP, and then force those 
to cover only the _one_ user-accessible page.

Something like

	#define FIXADDR_USER_START (fix_to_virt(FIX_VSYSCALL))
	#define FIXADDR_USER_END (FIXADDR_USER_START + PAGE_SIZE)

should work. In that case you can drop the page table testing, since we 
"know" it is safe.

But I'm too lazy to test, so please send a tested patch,

		Linus