On 08/27/2010 02:06 PM, Jan Kiszka wrote:
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.
I forgot them already. What was that, exception during IRET?
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).
I'd really like to avoid the timer. But I forgot all the details around
this, I'll have to re-learn them so I can actually compare the two options.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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