Re: KVM call minutes for Sept 21

["Nadav Har'El" <nyh@math.technion.ac.il>]

On Wed, Sep 22, 2010, Gleb Natapov wrote about "Re: KVM call minutes for Sept 21":
> There is only one outstanding serious issue from my point of view: event
> injection path. I want it to be similar to how nested SVM handles it. I
> don't see why it can't be done the same way for VMX too. The way nested SVM
> does it looks cleaner and making code paths similar will allow us to
> consolidate the logic in common code later. This issue is too
> fundamental to be fixed after merge IMHO. Other nitpicks about missing
> checks that real HW does, but emulation doesn't can be fixed any time
> after merge.

I'll try my best to accomodate your request, but I tried to explain in my
previous mails (and so dir Orit Wasserman in her mails last year, by the way -
I found a long thread in the mailing list...) that there appears to be a
fundemental additional complexity in VMX that doesn't exist in SVM. In VMX,
you might have to inject another exception (IDT_VECTORING_INFO_FIELD) at the
same time that you're already trying to inject a page fault to L1, and this
doesn't appear (?) to exist in SVM.
However, since I didn't write this code myself, and didn't encounter all the
problems myself, I still want to try to see whether I can get "cleaner" code
to actually work. But I want it to be really cleaner - not just remove one
somewhat-ugly intervention from vmx_complete_interrupts() and move it to an
even uglier intervention somewhere else.

In any case, while I obviously agree that it's your prerogative not to merge
code that you consider ugly, I still don't see any particular problem to start
with the current, working, code, and fix it later. It's not like we can never
change this code after it's in - it's clearly marked with if(nested) and
doesn't effect anything in the non-nested path.

> I think the question was "why do we need nested virtualization" ;)

Then why was nested SVM merged in the first place? Isn't it too late to
ask this question now? :-)

Anyway, I tried to answer this question in my previous email.
I'm not sure what more I can say to answer this question better.

Thanks,

Nadav.

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Nadav Har'El                        |   Wednesday, Sep 22 2010, 15 Tishri 5771
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