Re: GGI Project Unhappy On Linux
H. Peter Anvin (hpa@transmeta.com)
28 Mar 1998 14:50:39 GMT
Followup to: <Pine.LNX.3.96.980328150225.8094A-100000@vip.maestro.com.pl>
By author: Marek Habersack <grendel@vip.maestro.com.pl>
In newsgroup: linux.dev.kernel
>
> Hmm... It's enormous. The ring-0 code can do anything to your machine
> including memory management, LDT/GDT/IDT management, virtual memory management
> - everything your CPU and your hardware is capable of. The IOPL 3 merely
> (yeah...) allows the application to output to any of the ports of your
> hardware. That can crash the system, but usually the application are not
> allowed to access ALL ports - the IOPL at the end of the TSS is used to
> enable/disable access to the hardware ports. So the graphics application is
> allowed to trash only the video card registers - that can only hurt your
> display (unless your video card is buggy and freezes the bus ;-))
>
No, IOPL >= CPL means access to *ALL* ports permitted, as well as
CLI/STI and stuff. IOPL < CPL means that the I/O permission bitmap is
consulted, and CLI/STI trap.
-hpa
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