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

[Gleb Natapov <gleb@xxxxxxxxxx>]

On Tue, Jan 17, 2012 at 05:56:50PM +0530, Srivatsa Vaddagiri wrote:
> * Gleb Natapov <gleb@xxxxxxxxxx> [2012-01-17 11:14:13]:
> 
> > > 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.
> > > 
> > Just kick vcpu out of a guest mode and adjust rip to point after HLT on
> > next re-entry. Don't forget to call vmx_clear_hlt().
> 
> Looks bit hackish to me compared to having another hypercall to yield!
> 
Do not see anything hackish about it. But what you described above (the
part I replied to) is not another hypercall, but yet another NMI source
and special handling in a guest. So what hypercall do you mean?

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

--
                        Gleb.

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