On 09/19/2011 06:22 PM, Marcelo Tosatti wrote:
On Mon, Sep 19, 2011 at 06:09:39PM +0300, Avi Kivity wrote:
> On 09/19/2011 05:54 PM, Marcelo Tosatti wrote:
> >On Mon, Sep 19, 2011 at 05:30:27PM +0300, Avi Kivity wrote:
> >> On 09/19/2011 04:54 PM, Marcelo Tosatti wrote:
> >> >> >>
> >> >> >> Yes, due to NMI-blocked-by-STI. A really touchy area.
> >> >> >And we don't need the window exit notification then? I don't
understand
> >> >> >what nmi_in_progress is supposed to do here.
> >> >>
> >> >> We need the window notification in both cases. If we're
recovering
> >> >> from STI, then we don't need to collapse NMIs. If we're
completing
> >> >> an NMI handler, then we do need to collapse NMIs (since the queue
> >> >> length is two, and we just completed one).
> >> >
> >> >I don't understand what is the point with nmi_in_progress, and the
above
> >> >hunk, either. Can't inject_nmi do:
> >> >
> >> >if (nmi_injected + atomic_read(nmi_pending)< 2)
> >> > atomic_inc(nmi_pending)
> >> >
> >> >Instead of collapsing somewhere else?
> >>
> >> We could. It's not atomic though - two threads executing in
> >> parallel could raise the value to three. Could do a cmpxchg loop
> >> does an increment bounded to two. I guess this is a lot clearer,
> >> thanks.
> >>
> >> >You'd also have to change
> >> >nmi_injected handling in arch code so its value is not "hidden", in
> >> >complete_interrupts().
> >>
> >> Or maybe make raising nmi_injected not decrement nmi_pending. So:
> >>
> >> nmi_pending: total number of interrupts in queue
> >> nmi_injected: of these, how many are currently being injected
> >>
> >> yes?
> >
> >Yes, at the expense of decrementing on subarch code (which is fine,
> >apparently).
> >
>
> Hm, we have no place to decrement.
Decrement when setting nmi_injected = false, increment when setting
nmi_injected = true, in vmx/svm.c.
That gives a queue length of 3: one running nmi and nmi_pending = 2.
> We need to do that when IRET
> executes, but we don't want to request an NMI window exit in the
> common case of nmi_pending = 1.
Do not enable nmi window if nmi_injected = true?
We have to, since we need a back-to-back nmi if the queue length > 1
(including the running nmi).
--
error compiling committee.c: too many arguments to function
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