Re: [PATCH 1/1] Disable GUEST_INTR_STATE_STI flag before injecting NMI to guest on VMX

[Jan Kiszka <jan.kiszka@siemens.com>]

Avi Kivity wrote:
>   On 08/27/2010 11:39 AM, Jan Kiszka wrote:
>> AMD does not differentiate between MOV-SS and STI interrupt shadows.
>>
>> But AMD has its own NMI problems as it does not allow to trap after
>> IRET-from-NMI and requires magic dances which are partly broken in KVM.
>> I'm leaning towards NMI window emulation via the workaround we use for
>> older Intel CPUs without NMI window trapping as well.
> 
> Can you elaborate?

Basically the issues you found regarding our single-step-based
workaround. Moreover, we cannot easily prevent that TF set by the NMI
code leaks onto the guest's stack.

Jörg and I stuck heads together about this during LinuxCon. We came to
the conclusion that we either have to emulate the instruction that
delays NMIs (ie. _every_ possible instruction for the interrupt shadow
case) or fall back to the VMX workaround based on interrupt window
trapping and an emergency timeout (much simpler, but not really correct).

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux