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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.04.17 at 16:17, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 19/04/17 15:06, Jan Beulich wrote:
>>>>> On 19.04.17 at 15:49, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> If a PV kernel is aware of UMIP and turns UMIP on, #GPs from userspace
>>> should be bounced to the kernel, and #GPs from kernel space (as it is
>>> ring-deprivileged) must be emulated and execute successfully.
>>>
>>> If Xen is using UMIP to protect itself, it needs to emulate and fake up
>>> the information to both guest userspace and kernelspace.
>>>
>>> If both Xen and the PV kernel turn on UMIP, Xen needs to bounce
>>> userspace #GPs to the guest kernel, and fake up information for the
>>> guest kernel.
>> I disagree in one point: If the guest kernel enabled UMIP, it being
>> PV it should take care not to execute any of the covered insns (it
>> has no use for them anyway). I see no reason to emulate anything
>> in that case - emulation is needed only to keep _unaware_
>> environments working.
> 
> That will involve someone ensuring that new PVops get introduced and used.
> 
> Amongst other things, the current Linux doublefault handler uses sgdt.

But a PV guest would never get to see a #DF.

Jan


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