powerpc/64s: implement arch-specific hardlockup watchdog

Implement an arch-speicfic watchdog rather than use the perf-based
hardlockup detector.

The new watchdog takes the soft-NMI directly, rather than going through
perf.  Perf interrupts are to be made maskable in future, so that would
prevent the perf detector from working in those regions.

Additionally, implement a SMP based detector where all CPUs watch one
another by pinging a shared cpumask.  This is because powerpc Book3S
does not have a true periodic local NMI, but some platforms do implement
a true NMI IPI.

If a CPU is stuck with interrupts hard disabled, the soft-NMI watchdog
does not work, but the SMP watchdog will.  Even on platforms without a
true NMI IPI to get a good trace from the stuck CPU, other CPUs will
notice the lockup sufficiently to report it and panic.

[npiggin@gmail.com: honor watchdog disable at boot/hotplug]
  Link: http://lkml.kernel.org/r/20170621001346.5bb337c9@roar.ozlabs.ibm.com
[npiggin@gmail.com: fix false positive warning at CPU unplug]
  Link: http://lkml.kernel.org/r/20170630080740.20766-1-npiggin@gmail.com
[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20170616065715.18390-6-npiggin@gmail.com
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Tested-by: Babu Moger <babu.moger@oracle.com>	[sparc]
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/kernel/exceptions-64s.S

@@ -1314,6 +1314,31 @@ EXC_REAL_NONE(0x1800, 0x100)
 EXC_VIRT_NONE(0x5800, 0x100)
 #endif
 
+#if defined(CONFIG_HARDLOCKUP_DETECTOR) && defined(CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH)
+
+#define MASKED_DEC_HANDLER_LABEL 3f
+
+#define MASKED_DEC_HANDLER(_H)				\
+3: /* soft-nmi */					\
+	std	r12,PACA_EXGEN+EX_R12(r13);		\
+	GET_SCRATCH0(r10);				\
+	std	r10,PACA_EXGEN+EX_R13(r13);		\
+	EXCEPTION_PROLOG_PSERIES_1(soft_nmi_common, _H)
+
+EXC_COMMON_BEGIN(soft_nmi_common)
+	mr	r10,r1
+	ld	r1,PACAEMERGSP(r13)
+	ld	r1,PACA_NMI_EMERG_SP(r13)
+	subi	r1,r1,INT_FRAME_SIZE
+	EXCEPTION_COMMON_NORET_STACK(PACA_EXGEN, 0x900,
+			system_reset, soft_nmi_interrupt,
+			ADD_NVGPRS;ADD_RECONCILE)
+	b	ret_from_except
+
+#else
+#define MASKED_DEC_HANDLER_LABEL 2f /* normal return */
+#define MASKED_DEC_HANDLER(_H)
+#endif
 
 /*
  * An interrupt came in while soft-disabled. We set paca->irq_happened, then:
@@ -1336,7 +1361,7 @@ masked_##_H##interrupt:					\
 	lis	r10,0x7fff;				\
 	ori	r10,r10,0xffff;				\
 	mtspr	SPRN_DEC,r10;				\
-	b	2f;					\
+	b	MASKED_DEC_HANDLER_LABEL;		\
 1:	cmpwi	r10,PACA_IRQ_DBELL;			\
 	beq	2f;					\
 	cmpwi	r10,PACA_IRQ_HMI;			\
@@ -1351,7 +1376,8 @@ masked_##_H##interrupt:					\
 	ld	r11,PACA_EXGEN+EX_R11(r13);		\
 	GET_SCRATCH0(r13);				\
 	##_H##rfid;					\
-	b	.
+	b	.;					\
+	MASKED_DEC_HANDLER(_H)
 
 /*
  * Real mode exceptions actually use this too, but alternate