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

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

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?  :)

Thanks
Yu

> > And if the instructions are triggered in dom0 user space, the spec
> > requires a #GP
> > fault, and we can return 0 to the application in the #GP fault handler,
> > is it OK?
> Yes, I think so. But the fundamental rule is - make it match what
> native Linux does in that case.
>
> Jan
>
>
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