Re: [PATCH 2/4] kvm: svm: Enable UMIP feature on AMD

[Andy Lutomirski]

On Fri, Nov 1, 2019 at 10:33 AM Moger, Babu <Babu.Moger@xxxxxxx> wrote:
>
> AMD 2nd generation EPYC processors support UMIP (User-Mode Instruction
> Prevention) feature. The UMIP feature prevents the execution of certain
> instructions if the Current Privilege Level (CPL) is greater than 0.
> If any of these instructions are executed with CPL > 0 and UMIP
> is enabled, then kernel reports a #GP exception.
>
> The idea is taken from articles:
> https://lwn.net/Articles/738209/
> https://lwn.net/Articles/694385/
>
> Enable the feature if supported on bare metal and emulate instructions
> to return dummy values for certain cases.

What are these cases?