arm/arm64 HARDLOCKUP Detector and PERF NMI support

[mark.rutland@arm.com (Mark Rutland)]

Hi,

On Sat, Jan 09, 2016 at 04:13:48PM -0800, Mario Smarduch wrote:
> I'm trying to get HARDLOCKUP detector to work on arm (on foundation
> model and Juno, but armv7 should have the same issue). Turns out there is no
> PERF NMI support (HAVE_PERF_EVENTS_NMI), which I guess would be PMU NMI - I
> tested overflow on cycle counter and PMU interrupts can be masked. HARDLOCKUP
> assumes perf interrupts are non-maskable and uses the PMU to program an NMI to
> detect hard lockup and that in turn drives softlockup detection.
> 
> Is there something, someplace in ARM manuals that addresses this, searched the
> manuals but couldn't find anything?
> 
> Or other approaches that I'm not aware off or have floated on the mailing list.

Russell and Daniel did some work [1,2] to use FIQs as NMIs on arm, for
backtracing and PMU overflow.

For arm64 the kernel always runs on the non-secure side, so we don't
expect to have access to FIQ. It's possible to implement NMIs using
priorities (which it looks like Daniel was looking into [3]).

Thanks,
Mark.

[1] http://thread.gmane.org/gmane.linux.ports.arm.kernel/353795/
[2] http://www.linaro.org/blog/core-dump/debugging-arm-kernels-using-nmifiq/
[3] https://git.linaro.org/people/daniel.thompson/linux.git/shortlog/refs/heads/dev/arm64_nmi-v5