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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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