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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

> 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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