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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

32bit PV guest kernels execute in ring 1.
64bit PV guest kernels execute in ring 3.

~Andrew

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