[Xen-devel] Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

[Avi Kivity <avi@xxxxxxxxxx>]

On 09/14/2011 05:49 PM, Andi Kleen wrote:
> On Wed, Sep 14, 2011 at 10:00:07AM +0300, Avi Kivity wrote:
> >  On 09/13/2011 10:21 PM, Don Zickus wrote:
> >  >Or are you saying an NMI in an idle system will have the same %rip thus
> >  >falsely detecting a back-to-back NMI?
> >  >
> >  >
> >
> >  That's easy to avoid - insert an instruction zeroing the last nmi_rip
> >  somewhere before or after hlt.  It's always okay to execute such an
> >  instruction (outside the nmi handler itself), since nmi_rip is meant to
> >  detect a "no instructions executed" condition.
>
> At least for classic hlt there is no simple "after hlt" because it's all
> interrupt handlers and exceptions and everything else that can interrupt
> combined.
If an NMI hits in an interrupt handler, or in the "after hlt" section 
before the write-to-last-nmi-rip, then we'll see that %rip has changed.  
If it hits after the write-to-last-nmi-rip instruction (or in the hlt 
itself), then we'll also see that %rip has changed, due to the effect of 
that instruction.
--
error compiling committee.c: too many arguments to function


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