[Info-vax] Intel proposal to simplify x86-64

[Johnny Billquist]

On 2023-06-07 01:07, Scott Dorsey wrote:
> Johnny Billquist  <bqt at softjar.se> wrote:
>> On 2023-06-06 19:55, Scott Dorsey wrote:
>>> John Dallman <jgd at cix.co.uk> wrote:
>>>> In article <63a25e5a-2001-451b-b8a7-d6d9e74b02f9n at googlegroups.com>,
>>>> xyzzy1959 at gmail.com (John Reagan) wrote:
>>>>
>>>>> Other than an impact on the boot loader due to the change in
>>>>> startup mode, it has essentially no impact on OpenVMS
>>>>>
>>>>> OpenVMS does not use ring 1 or 2.  The 64-bit mode PTEs don't
>>>>> include support for ring 1 or 2 today, just ring 0 and 3.
>>>>
>>>> Thanks, glad to hear it.
>>>
>>> I'm not necessarily glad to hear it because I like the idea of keeping
>>> device drivers in a different ring than user processes or kernel....
>>
>> Hmm. Am I misremembering something? As far as I can recall, device
>> drivers in VMS (at least on VAX) are running in kernel mode. RMS in EXEC
>> and DCL in SUPER (or was it the other way around?).
> 
> Yes.  It's a shame.  When the new i386 rings came out I was thinking
> "Wow, we could do Honeywell-style stuff and it's not a mess like the
> 286 but... then nobody ever did.

Well. If you want full isolation between different parts of the kernel, 
going fully microkernel and message passing and all that, it's perfectly 
doable on pretty much any hardware. It's just that in general, whenever 
it has been done, performance always suffer. Which is why pretty much 
noone is doing it. And it's not because of issues in the hardware that 
it suffers. It's just that you can't avoid a lot more overhead when 
doing things this way. A lot of data copying first and foremost.

I guess Honeywell did, but can't say they were overly successful. MACH 
also did, but that part seems to not live on anywhere.

   Johnny