Re: [PATCH v5 2/5] KVM: VMX: Register a new IPI for posted interrupt

[Ingo Molnar <mingo@kernel.org>]

* Gleb Natapov <gleb@redhat.com> wrote:

> On Fri, Mar 08, 2013 at 03:05:45PM +0100, Ingo Molnar wrote:
> > 
> > * Gleb Natapov <gleb@redhat.com> wrote:
> > 
> > > On Fri, Mar 08, 2013 at 02:26:25PM +0100, Ingo Molnar wrote:
> > > > 
> > > > * Yang Zhang <yang.z.zhang@intel.com> wrote:
> > > > 
> > > > > diff --git a/arch/x86/kernel/irqinit.c b/arch/x86/kernel/irqinit.c
> > > > > index 6e03b0d..2329a54 100644
> > > > > --- a/arch/x86/kernel/irqinit.c
> > > > > +++ b/arch/x86/kernel/irqinit.c
> > > > > @@ -205,6 +205,10 @@ static void __init apic_intr_init(void)
> > > > >  
> > > > >  	/* IPI for X86 platform specific use */
> > > > >  	alloc_intr_gate(X86_PLATFORM_IPI_VECTOR, x86_platform_ipi);
> > > > > +#ifdef CONFIG_HAVE_KVM
> > > > > +	/* IPI for KVM to deliver posted interrupt */
> > > > > +	alloc_intr_gate(POSTED_INTR_VECTOR, kvm_posted_intr_ipi);
> > > > > +#endif
> > > > 
> > > > Please avoid wasting an IDT entry by reusing x86_platform_ipi.
> > > > 
> > > > A KVM guest is in essence one type of 'x86 platform', and this callback is used 
> > > > by hardware platforms, so collision is not an issue AFAICS.
> > > 
> > > This is IPI send by a host though.
> > 
> > But received on the guest side, right?
> 
> Not directly. If CPU that receives it happens to run in a guest mode it makes VMX 
> to re-evaluate pending interrupt and inject one if possible without vmexit.  If 
> CPU is not in a guest mode the handler for the IPI is called in a host mode and 
> does nothing. Guest code is unaware of the existence of that IPI.

Ok, I guess a separate IPI is fine (and better) in this case then.

Thanks,

	Ingo