Re: [Xen-devel] Communication between HVM and dom0 through the Hypervisor

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> > It it possible to arrange for a VMEXIT to occur on int 0x80
> > (which IIRC is the
> > Linux system call...  I guess VT-x would also be able to
> > intercept sysenter)?
> > That way the guest wouldn't have to be modified to notify
> > Xen.  Xen would
> > then have to e.g. share a ring buffer with dom0 regarding
> > events of this
> > nature for each domain.  You could hack something up so that
> > the guest
> > blocked on each syscall until dom0 acknowledged it...
>
> Now,that's a brilliant idea. Why didn't I think of that.
>
> Only one minor problem: It will only work for INT n instructions (but
> since it's possible to hide SYSENTER/SYSCALL instrutions from the guest
> via CPUID intercept, it can at least for 32-bit be forced to only do INT
> 80h calls), and only on AMD processors (this is more of a problem, as
> the original post talks about Intel processors). Intel processors don't
> allow intercepts of INT n instructions. Neither processor allow
> intercepts of SYSENTER/SYSCALL instructions. [It's still a very good
> idea, and I wish I had at least THOUGHT of it!]

Perhaps on intel, something could be bodged together?  E.g. intercept loading 
the IDT and replace the handler for the int n you're interested in with 
something that'll cause a trap?  I'm not really clear out sysenter etc 
actually works, so not so sure about that.

I did read through the VT-x / VT-i manuals at some stage, but it's a long time 
ago and things are a bit hazy now :-)

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel