Re: [Qemu-devel] [PATCH 0/2 v3] kvm: notify host when guest panicked

[Anthony Liguori]

On 03/15/2012 06:46 AM, Avi Kivity wrote:
> On 03/15/2012 01:25 PM, Jan Kiszka wrote:
> > > >
> > > There was such vm exit (KVM_EXIT_HYPERCALL), but it was deemed to be a
> > > bad idea.
> >
> > BTW, this would help a lot in emulating hypercalls of other hypervisors
> > (or of KVM's VAPIC in the absence of in-kernel irqchip - I had to jump
> > through hoops therefore) in user space. Not all those hypercall handlers
> > actually have to reside in the KVM module.
>
> That is true.  On the other hand the hypercall ABI might go to pieces if
> there was no central implementation.

Just declare that outl 0x505 is a megaultracall and s/vmcall/outb/g and call it 
a day.

The performance difference between vmcall and outl is so tiny compared to the 
cost of dropping to userspace that it really doesn't matter which instruction is 
used.

Regards,

Anthony Liguori

>