Xen devel - Sep 2005 - RE: frontend and backend devices and differenttypes of hw - pci for example

> While I''m on the subject, I''d personally like to see
guests
> granted IO access slightly differently.  There are two ways 
> to grant IO access on x86: change the IOPL (giving the guest 
> access to all IO ports) or set IO bits in the TSS (giving 
> fine grained control).  The problem with the latter is that guest
> *apps* will be able to access the hardware; essentially x86 
> gives you coarse grained control and ring-level protection, 
> or vice-versa.
> 
> Since people often like to partition their systems using Xen, 
> I don''t really like giving apps easy access to the hardware 
> in this way.  I''d like to have the option of trapping IO port 
> writes in Xen and verifying the guest''s IO privileges in 
> software, then emulating the write. 
That''s how it works in -unstable today...

Ian

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> > Since people often like to partition their systems using Xen,
> > I don''t really like giving apps easy access to the hardware
> > in this way.  I''d like to have the option of trapping IO port
> > writes in Xen and verifying the guest''s IO privileges in
> > software, then emulating the write.
>
> That''s how it works in -unstable today...
Ah, so it is.  IOPL emulation works correctly - cute :-)  I actually vaguely 
remember the checkin but didn''t look at the diff at the time.

Thanks,
Mark

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