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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan

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




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