Re: [Qemu-devel] [PATCH] MSI / MSIX injection for Xen HVM

[Stefano Stabellini]

On Thu, 1 Mar 2012, Paolo Bonzini wrote:
> Il 01/03/2012 15:06, Stefano Stabellini ha scritto:
> >> > This is not a NACK, but I can't help asking.  Perhaps the fake Xen
> >> > interrupt controller is a bit too simplistic?  You can add a memory
> >> > region corresponding to the APICs and trap writes in that region.
> >> > Writes coming from QEMU are MSIs and can be injected to the hypervisor,
> >> > writes coming from the VM will be trapped by Xen before going out to 
> >> > QEMU.
> >  
> > That is a good point actually: we already have lapic emulation in Xen,
> > it makes sense to have apic-msi in Xen too.
> > We would still need the changes to msi_notify and msix_notify though.
> 
> Why?  The stores would just go to the Xen interrupt controller MMIO area
> which then does the xc_hvm_inject_msi.
 
Because msi(x)_notify is called by QEMU's emulated devices: it is not
possible from QEMU to cause an emulation trap in Xen on behalf of the
guest.