Re: [Xen-ia64-devel] RE: [PATCH]: disable handling of legacy privified insns

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Vendredi 17 Mars 2006 20:53, Magenheimer, Dan (HP Labs Fort Collins) a 
écrit :
> > From: Tristan Gingold [mailto:Tristan.Gingold@xxxxxxxx]
> > Sent: Friday, March 17, 2006 2:48 AM
> > To: Magenheimer, Dan (HP Labs Fort Collins)
> > Subject: Re: [Xen-ia64-devel] RE: [PATCH]: disable handling
> > of legacy privified insns
> >
> > Just a question: why hyperprivops need ic=0/ic=1 ?
> > Since they can only occur in CPL=2, Xen could check CPL
> > instead of ic ?
>
> Answering on-list for documentation to community...
>
> Break instructions and the full range of break immediate
> values are reserved for the guest.  Linux/ia64 only uses
> one break immediate value for system calls, however other
> operating systems (or future changes to Linux/ia64) may
> use other break immediate values.  Thus it is unsafe for
> Xen/ia64 to assume any specific break immediate value
> is not used by a guest.
This is what I don't understand.

Hyperprivops should only occur in Linux, shouldn't them ?

The Linux kernel doesn't use the break instructions for itself, does it ?

So, if I am correct the linux kernel could use break insns without ic=0/ic=1 
for hyperprivops.

I really think this could work for linux.
What about other OS ?  I don't see why they would use break in kernel mode.
The only exception may be debugger/single stepping.

Tristan.



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