Re: [PATCH 2/2] KVM: SVM: check for progress after IRET interception

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

On 2011-02-03 17:20, Avi Kivity wrote:
> On 02/03/2011 06:14 PM, Jan Kiszka wrote:
>> On 2011-02-03 16:58, Avi Kivity wrote:
>>>  On 02/03/2011 05:55 PM, Jan Kiszka wrote:
>>>>>
>>>>>   What's an interrupt window without IRET interception?
>>>>
>>>>  I don't the details, but I thought you could get something like an
>>>>  interrupt-window-open interception by (fake-)injecting an IRQ and
>>>>  intercepting on VIRQ acceptance. That will not work if returning to and
>>>>  staying in irq-disabled guest code, therefore the timeout, but it should
>>>>  be most efficient (specifically if the guest uses NMIs for things like
>>>>  perf).
>>>>
>>>
>>>  Since NMIs are used to break out of irq-disabled regions (watchdog, NMI
>>>  IPIs during reboots) I'm wary of such a solution.
>>
>> Right, but we already use it for Intel. The timeout ensures that you
>> can't get stuck forever. I think Xen works this way as well (minus the
>> timeout - last time I checked).
> 
> Only without vnmi support, yes?  In that case, we can't do any better.  
> In this case, we can, and we should, even at the expense of performance 
> or ridiculous complexity.

OK, then I guess we should explore the single-step approach and make it
waterproof. It's likely still much simpler than iret emulation.

Jan

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