On Sun, Oct 29, 2006 at 09:13:38PM +0100, Christian Biere wrote:
> John Nemeth wrote:
> >      What does an i386-compatible MMU provide that the i386 MMU didn't?
> 
> It seems memory write-protection at cpl0 (ring0) doesn't work in an i386 MMU.

Define 'work'!

From pages 6-21 of the 80386 Programmer's Reference Maunal (1986):

Section 6.4.1.1
"The current level (U or S) is related to the CPL. If the CPL is 0, 1, or 2
the processor is executing at supervisor level. If CPL is 3, theprocessor is
executing at user level.

Section 6.4.1.2

When the processor is executing at supervisor level, all pages are both
readable and writable.

I don't have the 486 book!

	David

-- 
David Laight: david@l8s.co.uk