> On Tue, 19 Dec 2000, John Summerfield wrote:
> > [EMAIL PROTECTED] said:
> > > Well, I don't see the benefit of using ring1 in stead of ring0. The
> > > protection problem remains...
> >
> > Some things cannot be run in ring1; an attempt to so so generates a general
>
> > exception..
>
> What things? IIRC, ring0/1/2 are mostly identical except that you can
> play with DPLs. x86 has three supervisor levels and one user level.
I don't have a list, but I did look up HLT yesterday. It's one byte, only
executes in ring0.
In other levels, it can be used as a kind of system call (as has been done for
many years on other architectures).
> > Then ring0 code can take a look and decide whether to emulate or kill, and
> if
> > emulation, then what kind of emulation (in some circumstances, 'device not
> > present" might be more appropriate than doing something a real device would
> ).
>
> This doesn't solve any of the performance issues with the current
> system... it would just complicate it more.
I've been wondering whether writing a VM to run under Linux is the best way to
achieve it; the bext VM I know is IBM's VM/ESA, written to run "on the metal."
OS/2 has a pretty good one too; it runs DOS including DRDOS and (probably)
CP/M-86. But it's only 8086 using the V86 box. Runs well though, and can run
Windows 3.1 drivers.
--
Cheers
John Summerfield
http://www2.ami.com.au/ for OS/2 & linux information.
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