Far and near pointers on the 80286 and later

Joe Pfeiffer wrote:
One of the many clever features of the x86 is an IO protection bitmap,
permitting a process at any level (even user level) to access hardware
directly, without a kernel trap.

Oh yes, you're right IOPL allowed that, but my impression was that IOPL
could not differentiate between ring levels. That is, if you allowed
IOPL to anything other than ring 0, then all other rings from 1 through
3 would have direct access to the i/o ports in that map. You couldn't
for example, limit the access only upto ring 1.

Yousuf Khan

Yousuf Khan wrote:
Joe Pfeiffer wrote:
One of the many clever features of the x86 is an IO protection bitmap,
permitting a process at any level (even user level) to access hardware
directly, without a kernel trap.

Oh yes, you're right IOPL allowed that, but my impression was that IOPL
could not differentiate between ring levels. That is, if you allowed
IOPL to anything other than ring 0, then all other rings from 1 through
3 would have direct access to the i/o ports in that map. You couldn't
for example, limit the access only upto ring 1.


I haven't looked at this in a while, but I believe IOPL 0 allowed that
ring and any lower to have access. That is, if IOPL=1, then 0 and 1
could access H/W, 2 and 3 couldn't.

BTW, I see OS/2 may be making a comeback;-)

Yousuf Khan writes:

Joe Pfeiffer wrote:
One of the many clever features of the x86 is an IO protection bitmap,
permitting a process at any level (even user level) to access hardware
directly, without a kernel trap.

Oh yes, you're right IOPL allowed that, but my impression was that
IOPL could not differentiate between ring levels. That is, if you
allowed IOPL to anything other than ring 0, then all other rings from
1 through 3 would have direct access to the i/o ports in that map. You
couldn't for example, limit the access only upto ring 1.

The bitmap is per-process, so if the process has the access then it has
it at whatever level it's running at.
--
As we enjoy great advantages from the inventions of others, we should
be glad of an opportunity to serve others by any invention of ours;
and this we should do freely and generously. (Benjamin Franklin)

In article ,
Joe Pfeiffer wrote:

Yousuf Khan writes:

Peter Flass wrote:
OS/2 uses three: one for the kernel, one for drivers, etc., and the
third for user programs.

Are you sure OS/2 actually uses that? The Intel architecture allowed
for upto 4 privilege rings (now it's 5 rings with
virtualization). However, most OS software never used more than 2
rings, highest (for OS & drivers) and lowest (for apps).

The reason I'm skeptical is because running drivers in anything other
than highest privilege level means you run into performance penalties,
since all hardware accesses by the driver will result in a exception
fault requiring a redirection through the OS first. Not great if your
driver has to respond to hardware signals fast.

One of the many clever features of the x86 is an IO protection bitmap,
permitting a process at any level (even user level) to access hardware
directly, without a kernel trap.

To clever by half, judging by the results.

--
A computer without Microsoft is like a chocolate cake without mustard.

I haven't looked at this in a while, but I believe IOPL 0 allowed
that ring and any lower to have access. That is, if IOPL=1, then 0
and 1 could access H/W, 2 and 3 couldn't.

BTW, I see OS/2 may be making a comeback;-)

Well, according to the OSFree roadmap ... (-:

The article that you mentioned before seemed to be discussing the
Workplace Shell more than OS/2 itself.

Here's some computer folklo Esther Schindler reported on 2007-12-07
that IBMers had tolder her that some of the OS/2 source code has been
lost, in the move from Boca Raton to Austin.

"Jonathan de Boyne Pollard" wrote
in message
ard.localhost...


I haven't looked at this in a while, but I believe IOPL 0 allowed that
ring and any lower to have access. That is, if IOPL=1, then 0 and 1
could access H/W, 2 and 3 couldn't.

BTW, I see OS/2 may be making a comeback;-)

Well, according to the OSFree roadmap ... (-:

The article that you mentioned before seemed to be discussing the
Workplace Shell more than OS/2 itself.

Here's some computer folklo Esther Schindler reported on 2007-12-07
that IBMers had tolder her that some of the OS/2 source code has been
lost, in the move from Boca Raton to Austin.


It's not from IBM but OS/2 is available for current hardware
(renamed eComStation):

http://www.ecomstation.com/

I downloaded the demo just for fun and, wow! It's not bad at all!

Tom Lake

One of the many clever features of the x86 is an IO protection
bitmap, permitting a process at any level (even user level) to access
hardware directly, without a kernel trap.

To clever by half, judging by the results.

Which results?

Jonathan de Boyne Pollard wrote:


I haven't looked at this in a while, but I believe IOPL 0 allowed
that ring and any lower to have access. That is, if IOPL=1, then 0
and 1 could access H/W, 2 and 3 couldn't.

BTW, I see OS/2 may be making a comeback;-)

Well, according to the OSFree roadmap ... (-:

The article that you mentioned before seemed to be discussing the
Workplace Shell more than OS/2 itself.

Here's some computer folklo Esther Schindler reported on 2007-12-07
that IBMers had tolder her that some of the OS/2 source code has been
lost, in the move from Boca Raton to Austin.


There's a name from the past. I just spent quite a bit of time trying
to recall her name (finally successfully), when I saw Smack! listed by
BMTMicro. Didn't she write that one?

Tom Lake wrote:

"Jonathan de Boyne Pollard"
wrote in message
ard.localhost...


I haven't looked at this in a while, but I believe IOPL 0 allowed
that ring and any lower to have access. That is, if IOPL=1, then 0
and 1 could access H/W, 2 and 3 couldn't.

BTW, I see OS/2 may be making a comeback;-)

Well, according to the OSFree roadmap ... (-:

The article that you mentioned before seemed to be discussing the
Workplace Shell more than OS/2 itself.

Here's some computer folklo Esther Schindler reported on
2007-12-07 that IBMers had tolder her that some of the OS/2 source
code has been lost, in the move from Boca Raton to Austin.


It's not from IBM but OS/2 is available for current hardware
(renamed eComStation):

http://www.ecomstation.com/

I downloaded the demo just for fun and, wow! It's not bad at all!


I don't think they've been able to fix the kernel problems. I know
they've added a lot of drivers and applications. One of these days I'm
going to have to get a copy.

I haven't looked at this in a while, but I believe IOPL 0 allowed
that ring and any lower to have access. That is, if IOPL=1, then 0
and 1 could access H/W, 2 and 3 couldn't.

BTW, I see OS/2 may be making a comeback;-)

Well, according to the OSFree roadmap ... (-:

The article that you mentioned before seemed to be discussing the
Workplace Shell more than OS/2 itself.

Here's some computer folklo Esther Schindler reported on
2007-12-07 that IBMers had told her that some of the OS/2 source code
has been lost, in the move from Boca Raton to Austin.

There's a name from the past. I just spent quite a bit of time trying
to recall her name (finally successfully), when I saw Smack! listed by
BMTMicro. Didn't she write that one?

I've no idea. I've never heard of it. (-:

One thing that I know xe did write was a call to open-source SOM. Now
that's something that would be very helpful. Yes, NOM exists, but from
what I'm told it isn't binary compatible with SOM, which rather misses
one of the major points of using SOM.