Re: [Xen-devel] [PATCH RFC V4 5/5] Documentation/kvm : Add documentation on Hypercalls and features used for PV spinlock

[Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>]

* Avi Kivity <avi@xxxxxxxxxx> [2012-01-16 12:14:27]:

> > One option is to make the kick hypercall available only when
> > yield_on_hlt=1?
> 
> It's not a good idea to tie various options together.  Features should
> be orthogonal.
> 
> Can't we make it work?  Just have different handling for
> KVM_REQ_PVLOCK_KICK (let 's rename it, and the hypercall, PV_UNHALT,
> since we can use it for non-locks too).

The problem case I was thinking of was when guest VCPU would have issued
HLT with interrupts disabled. I guess one option is to inject an NMI,
and have the guest kernel NMI handler recognize this and make
adjustments such that the vcpu avoids going back to HLT instruction.

Having another hypercall to do yield/sleep (rather than effecting that
via HLT) seems like an alternate clean solution here ..

- vatsa


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