Re: [Xen-devel] about fully UMIP support in Xen

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 4/19/2017 10:09 PM, Andrew Cooper wrote:
> On 19/04/17 15:07, Jan Beulich wrote:
> > > > > On 19.04.17 at 15:58, <andrew.cooper3@xxxxxxxxxx> wrote:
> > > On 19/04/17 14:50, Yu Zhang wrote:
> > > > On 4/19/2017 9:34 PM, Jan Beulich wrote:
> > > > > > > > On 19.04.17 at 13:44, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > > > > > On 4/19/2017 7:19 PM, Jan Beulich wrote:
> > > > > > > > > > On 19.04.17 at 11:48, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > > > > > > > Does hypervisor need to differentiate dom0 kernel and its
> > > > > > > > user space?
> > > > > > > If we want to para-virtualize the feature, then yes. Otherwise
> > > > > > > we can't assume the guest kernel would deal with user mode faults,
> > > > > > > so we'd have to. Arguably there could be a non-default mode in
> > > > > > > which we don't (forcing such applications to get a signal or crash).
> > > > > > For UMIP is to be para-virtualized,  is it OK to give dom0 kernel the
> > > > > > physical value
> > > > > > if instructions are triggered in the kernel?
> > > > > Why would you want to special case Dom0 here? I don't see
> > > > > anything wrong with giving Dom0 the real values, but since you'll
> > > > > have to not give DomU-s the real values, you'd then add more
> > > > > code to treat Dom0 specially. Simply give everyone fake values.
> > > > Oh. So in such case should return 0 to the dom0 kernel I guess?
> > > >
> > > > Here come a dumb question: does other pv domain also run in ring 3 in
> > > > vmx root mode,
> > > > or simply in vmx non-root ring 0?  :)
> > > PV guests execute exclusively in non-root mode.
> > In root mode, you mean.
> I do.  (oops.  Sorry.)
Thanks a lot, Andrew & Jan.
And back to the schedule of this feature, are you working on it? Or any 
specific plan?
Is there anything we can do here in Intel?

B.R.
Yu


> ~Andrew
>
> > Jan
> >
> > > 32bit PV guest kernels execute in ring 1.
> > > 64bit PV guest kernels execute in ring 3.
> > >
> > > ~Andrew

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