Messages in this thread | | | Date | Fri, 17 Jul 1998 14:24:02 +0200 (METDST) | From | Gabriel Paubert <> | Subject | Re: I/O permissions for V86 tasks (Enhanced V86 Mode)? |
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On Thu, 16 Jul 1998, Kendall Bennett wrote:
> > And by the way, the answer to your previous question about IOPL is no, > > the Intel processor does not allow the V86 task to take notice of any IOPL > > so you are forced to do it via the bitmap. > > Actually this brings up another issue. I recall reading in Dr Dobb's > (I think) about the undocumented Pentium Enhanced V86 mode. One of > the features of this if I remember correctly is that you can enable > IOPL priveledges for V86 tasks rather than having to use a full 8Kb > I/O bitmap. > > Does anyone know any details of this, and if this has been looked > into for the V86 mode support in Linux? I am going to hunt through my > old issues to see if I can find the articles in question, and if the > info is enough I will try to hack the support for this into my kernel > sources. This would be the ideal solution if it would work, since > then we don't have to do anything special to get full I/O access for > V86 tasks (and I am sure this will make the DOSEMU crowd happier).
It won't work, this IOPL thing ony affects the interrupt flag (CLI/STI/PUSHF/POPF/IRET) and the interrupt redirection bitmap which allows int n instructions to be executed without being reflected from protected mode. But the I/O bitmap itself is not affected, it would be far too dangerous to allow access to any I/O port.
Gabriel.
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