Registering interrupt handler for performance counter overflow

[Eitan Kaplan <e.kaplan@columbia.edu>]

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Hi all,

I am a computer engineering student at Columbia University. This is my
first time writing to this list (please let me know if this isn't the place
for this type of question!).

I am working with a professor on a project to mitigate Spectre and Meltdown
(and other similar cache timing side-channel attacks).  We are using Xen
and modifying its source as a way of modeling the affect certain potential
hardware changes. As part of that project, we need to use the performance
counters to generate interrupts at certain microarchitectural events.  I
have successfully added into xen/arch/x86/setup.c a few lines to setup the
(Intel Sandy Bridge) performance counter control MSRs and set the counter
itself to a few below overflow.  All that's missing is a simple interrupt
handler that will reset the counter to a few below overflow (and perhaps do
some logging).

I am having trouble figuring out how to register my handler in Xen.  I
assume that I have to call request_irq(), but I am not sure how to set all
the arguments for that call.  Would anyone be able to give me any
pointers?  Suggestions or pointers to resources/examples for registering
interrupt handlers in Xen would be really helpful!

Alternatively, is there an existing interrupt handler that is already setup
for PMC overflow interrupts that I might be able to tweak?

Thank you!
Eitan Kaplan

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