Re: [Xen-ia64-devel] privilege level of PV domain

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Mon, Jun 25, 2007 at 08:34:02AM +0200, Jürgen Groß wrote:
> I've got a question about the emulation of cpl=0 of a PV-domain.
> Currently cpl=0 is emulated by using privilege level 2. Is there any special
> reason not to use privilege level 1?
>
> The reason for my question is the port of our mainframe operating system to
> xen/ia64. We are using three different privilege levels today and it would
> make the port much easier if we could keep this approach.
> This is only possible, if cpl=0 of the domU is mapped to privilege level 1
> by the hypervisor, of course.
> 
> If there is no architectural reason for using cpl=2 instead cpl=1, I would
> prepare some patches...

It's because the historical reason as long as I know.
Xen/ia64 owes to vBlades[1] very much and they chose cpl=2
for guest kernel and used cpl=1 for other purose.
Xen/IA64 inherited cpl=2 for guest and but hasn't used cpl=1 so far.
At this moment I don't see any architectural except it would
require tedious error prone code change.

[1] You can find vBlades paper easily on the net.
-- 
yamahata

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