Re: [Xen-devel] [PATCH v6] x86/monitor: Notify monitor if an emulation fails.

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 07/18/2017 01:09 PM, Andrew Cooper wrote:
> On 18/07/17 10:37, Petre Pircalabu wrote:
>> If case of a vm_event with the emulate_flags set, if the instruction
>> cannot be emulated, the monitor should be notified instead of directly
>> injecting a hw exception.
>> This behavior can be used to re-execute an instruction not supported by
>> the emulator using the real processor (e.g. altp2m) instead of just
>> crashing.
>>
>> Signed-off-by: Petre Pircalabu <ppircalabu@xxxxxxxxxxxxxxx>
> 
> There are many situations which end up failing an emulation with
> UNHANDLEABLE.
> 
> What exact scenario are you looking to catch?  Is it just instructions
> which aren't implemented in the emulator?

Instructions that are not implemented in the emulator are our main use
case for this, yes. In which case, we'd like a chance to be able to
single-step them (using altp2m), so that the guest will continue to run
even with an incomplete emulator.

We don't care about instructions that would have failed to run in both
scenarios (emulated or single-stepped). I'm not sure if there are other
cases in which an instruction, although supported by the emulator, would
fail emulation but pass single-stepping.


Thanks,
Razvan

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