Re: [Xen-devel] [PATCH 06/15] xen: trace IRQ enabling/disabling

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.06.17 at 01:42, <dario.faggioli@xxxxxxxxxx> wrote:
> On Thu, 2017-06-01 at 20:08 +0100, Andrew Cooper wrote:
>> By writing the trace record while interrupts are disabled, you do
>> prevent nesting in the general case (but not in NMIs/MCEs or the
>> irqsave() variants), 
>>
> Forgive the ignorance, what's special about NMIs/MCAs that is relevant
> for this?

NMI/#MC can nest nevertheless, so preventing nesting in the
common case doesn't mean you won't see nesting at all.

>> Does the logic cope with the fact that interrupt gates automatically
>> disable interrupts?
>> 
> Ah, right. No, it does not. I probably should mention this in the
> changelog. Any ideas of how to deal with that? If yes, I'm more than
> happy to fix this...

Well, respective entry points will need to update tracking state.
See how Linux has placed certain macros to that effect on
various entry paths.

Jan


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