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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Apr 10, 2013 at 01:32:41PM +0000, Zhang, Yang Z wrote:
> Konrad Rzeszutek Wilk wrote on 2013-04-10:
> > On Wed, Apr 10, 2013 at 02:51:41AM +0000, Zhang, Yang Z wrote:
> >> Konrad Rzeszutek Wilk wrote on 2013-04-10:
> >>> On Tue, Apr 09, 2013 at 02:01:27PM +0800, Yang Zhang wrote:
> >>>> From: Yang Zhang <yang.z.zhang@Intel.com>
> >>>> 
> >>>> The follwoing patches are adding the Posted Interrupt supporting to Xen:
> >>>> Posted Interrupt allows vAPIC interrupts to inject into guest directly
> >>>> without any vmexit.
> >>> 
> >>> Is there a mechanism for the guest to figure out whether this is exported?
> >> Expose it to guest? No.
> >> 
> >>> 
> >>> Right now the Linux PVHVM guests will use the event channel mechanism
> >>> (via the 0xf3 callback vector). This means that if we want to do IPIs
> >>> (RESCHEDULE_VECTOR or CALL_FUNCTION_*) we end up doing a vmexit - but
> >>> with this we should be able to do these inside the guest right?
> >> I am not familiar with PV staffs. Will event channel mechanism touch vAPIC? If
> > no, perhaps the answer is not.
> > 
> > No it won't. But any any inter-OS vectors (such as IPIs) would benefit
> > from vAPIC right? As in posting those vectors (assuming the destination
> > VCPU is running) would not cause an VMEXIT?
> Yes.
> 
> >> 
> >>> 
> >>> If so, is there a mechanism inside the guest to detect this and
> >>> use the HVM mechanisms for IPI?
> >> Why guest should aware of this? Current implementation already covers the
> > vIPI.
> > 
> > Not sure I understand you. What current implementation?
> I thought you mean the vIPI. Obviously, I am wrong. :(
> What does " HVM mechanisms for IPI " mean? 

'__default_send_IPI_dest_field' in the Linux code, which is
writting in the ICR2 field in the APIC.