Re: [V6][PATCH 4/6] x86, nmi: add in logic to handle multiple events and unknown NMIs

Jeremy Fitzhardinge
2011-09-28T17:12:59Z

On 09/28/2011 05:37 AM, Don Zickus wrote:
> On Wed, Sep 28, 2011 at 12:31:40PM +0200, Robert Richter wrote:
>> On 23.09.11 15:17:13, Don Zickus wrote:
>>> @@ -89,6 +89,15 @@ static int notrace __kprobes nmi_handle(unsigned int type, struct pt_regs *regs)
>>>
>>> handled += a->handler(type, regs);
>>>
>>> + /*
>>> + * Optimization: only loop once if this is not a
>>> + * back-to-back NMI. The idea is nothing is dropped
>>> + * on the first NMI, only on the second of a back-to-back
>>> + * NMI. No need to waste cycles going through all the
>>> + * handlers.
>>> + */
>>> + if (!b2b && handled)
>>> + break;
>> I don't think we can leave this in. As said, there are cases that 2
>> nmis trigger but the handler is called only once. Only the first would
>> be handled then, and the second get lost cause there is no 2nd nmi
>> call.
> Right. Avi, Jeremy what was your objection that needed this optimization
> in the first place?

My only interest in the NMI code is its use of spinlocks, which seem
inappropriate.

J