[Qemu-devel] Re: SVM emulation: EVENTINJ marked valid when a pagefault happens while issuing a software interrupt

[Erik van der Kouwe]

Hi,

Thankss for your answer.

> SVM always clears the vmcb.eventinj on vmrun because every exception is
> injected right after vmrun finished and cpu is in guest mode. It can
> happen (for example if taking the exception causes a page fault) that
> the vmcb.eventinj field is copied to vmcb.exit_int_info.

Yes, this s what I have been experiencing.

> In nested-svm you can get a valid exit_int_info when an interrupt or nmi
> is pending too. In the software implementation these intercepts are
> taken before the event is delivered and you find the event in
> vmcb.exit_int_info.
> This is not forbidden in the svm architecture and I have not found a
> hypervisor that has a problem with this different behavior. I have a
> patch here which changes this in nested-svm, but it introduces more
> problems than it fixes.

This is a ok, the problem is the event_inj field rather than the 
exit_int_info field. From what I've seen the SVM specification neither 
specifies that the CPU writes to this field nor does it explicitly 
forbid it. Given the unclarity of the specification it may safest to 
deal with this in the same way as the hardware does (although I don't 
know which way this is, it seems inuitively unlikely that the hardware 
would set event_inj to valid).

With kind regards,
Erik