Re: [PATCH 2/2] x86, apicv: Add Posted Interrupt supporting

Gleb Natapov
2013-01-31T13:38:39Z

On Thu, Jan 31, 2013 at 11:32:45AM -0200, Marcelo Tosatti wrote:
> On Thu, Jan 31, 2013 at 11:43:48AM +0200, Gleb Natapov wrote:
> > On Wed, Jan 30, 2013 at 09:03:11PM -0200, Marcelo Tosatti wrote:
> > > Posted interrupt patch:
> > > 2) Must move IN_GUEST_MODE assignment after local_irq_disable, in
> > > vcpu_enter_guest function. Otherwise:
> > >
> > > cpu0 vcpu1<->cpu1
> > >
> > > vcpu->mode = IN_GUEST_MODE
> > >
> > > if IN_GUEST_MODE == true
> > > send IPI
> > > local_irq_disable
> > >
> > > PIR not transferred to VIRR, misses interrupt.
> > >
> > cpu0 will set KVM_REQ_EVENT, so vmentry will be aborted after
> > local_irq_disable() by ->requests check.
>
> Yes, but you don't want KVM_REQ_EVENT+kick. It defeats the purpose
> of posted interrupts. You want
>
> if vcpu in guest mode
> send posted interrupt IPI
> else
> KVM_REQ_EVENT+kick
>
I am thinking:

set KVM_REQ_EVENT
if pi is enabled
send posted interrupt IPI
else
kick

> > > 3) Must check outstanding PIR notification bit unconditionally on
> > > every VM-entry, because:
> > >
> > > 1. local_irq_disable
> > > 2. vcpu->mode = IN_GUEST_MODE
> > > 3. vmenter
> > > 4. vmexit
> > > 5. vcpu->mode = OUTSIDE_GUEST_MODE
> > >
> > > If PIR-IPI-interrupt is sent between an event which triggers VM-exit
> > > (for example, an external interrupt due to a device), and step 5
> > > (assignment of vcpu->mode), the PIR->VIRR transfer before vmentry must
> > > be made.
> > Not sure I understand, but I think KVM_REQ_EVENT will cover that too.
>
> See above.
>
> > >
> > > 4) Today, an interrupt notification is cached on IRR until its delivered - further
> > > interrupt injection is not generating further interrupt notification
> > > bits. With PIR, behaviour changes: Its possible to have one bit in PIR and another
> > > on IRR APIC page (if timing is right). Is this harmless? Why?
> > >
> > >
> >
> > --
> > Gleb.

--
Gleb.