[Xen-devel] Question about evtchn_callback reentry

["Xu, Anthony" <anthony.xu@xxxxxxxxx>]

Hi Keir,

I have some questions about evtchn_callback,

As we know all external interrupts and events are deliver to dom0 by
evtchn_callback,

Are evtchn_callback reentered?

I mean when evtchn_callbacak is executing on dom0,

Another external interrupt or event may happen, can this event be
deliverred immediately?

I found __sti will set vcpu_info-> evtchn_upcall_mask=0, which permits
event deliverring.

and __sti may be called at any device driver. 

If evtchn_callback can be reentered, how does it hanlde external
interrupt privilege?

If there is no special handling, low privileged interrupt may
"interrupt" high privileged interrupt.


BTW,
I do see evtchn_callback reentry happen on IPF dom0, and that incur
about 5% performance degradation
with KB on VTI-domain compared to non_reentry.



Thanks,
Anthony

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