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Re: [Xen-devel] [PATCH 0/4] Add posted interrupt supporting

On Sat, 20 Apr 2013, Zhang, Yang Z wrote:
> Jan Beulich wrote on 2013-04-19:
> >>>> On 19.04.13 at 13:49, Stefano Stabellini 
> >>>> <stefano.stabellini@xxxxxxxxxxxxx>
> > wrote:
> >> I am also interested in this question and I cannot find a clear answer:
> >> when a guest vcpu wants to issue an IPI to another vcpu, will it trap
> >> into Xen? Or will everything work automagically?
> > 
> > For PV, obviously, this is done by a hypercall.
> > 
> > For HVM this ought to depend on the level of hardware assistance
> > in LAPIC virtualization: Traditionally, the involved LAPIC register
> > accesses would trap into the hypervisor. But with full APIC
> > virtualization, this should not be happening anymore.
> No. Actually, only self IPI will handled by hardware directly. All other 
> vIPIs still cause APIC write vmexit.

Thanks for the clarification, that answers my question.

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