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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

~Andrew

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