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

[Jürgen Groß <juergen.gross@xxxxxxxxxxxxxxxxxxx>]

Isaku Yamahata wrote:
> 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.

Thanks!
My plan is to make a patch first which uses a '#define' for the privilege
level instead the hard coded '2'. This should minimize a possible negative
impact.

Juergen

-- 
Juergen Gross                             Principal Developer
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