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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 19 Apr 2013, Jan Beulich wrote:
> >>> 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.

Right.

> But with full APIC virtualization, this should not be happening anymore.

Is this feature detectable on the guest side?
If so, we could probe it and only if it is available we could drop PV
IPIs in favor of the native IPI ops.

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