[PATCH] arm64: Decode information from ESR upon mem faults

On Wed, Jun 14, 2017 at 02:14:03PM +0100, Julien Thierry wrote:

When receiving unhandled faults from the CPU, description is very sparse.
Adding information about faults decoded from ESR.

Added defines to esr.h corresponding ESR fields. Values are based on ARM
Archtecture Reference Manual (DDI 0487B.a), section D7.2.28 ESR_ELx, Exception
Syndrome Register (ELx) (pages D7-2275 to D7-2280).

New output is of the form:
[  122.109118] Mem abort info:
[  122.111884]   Exception class = DABT (current EL)
[  122.116564]   IL = 32 bits
[  122.119242]   SET = 0
[  122.121507]   FnV = 0
[  122.123754]   EA = 0
[  122.125928]   S1PTW = 0
[  122.128347] Data abort info:
[  122.131212]   ISS[23:14] invalid

Is it still worth printing the ISS value here? I'm wondering about the
case where an old kernel runs on a new CPU and gets an abort that was
previously undefined.

[  122.134417]   CM = 0
[  122.136589]   WnR = 1

Hmm, this might get really confusing if multiple CPUs end up with their
prints interleaved. Perhaps having a print_unhandled_fault_info helper that
takes a prefix string (e.g. "Unhandled fault") and constructs the
information on one line would be preferable?

Then again, you could make the same argument about multi-line register
dumps, so perhaps I'm worrying too much here. Thoughts?

Will