powerpc/64s/interrupt: masked handler debug check for previous hard disable

Prior changes eliminated cases of masked PACA_IRQ_MUST_HARD_MASK
interrupts that re-fire due to MSR[EE] being enabled while they are
pending. Add a debug check in the masked interrupt handler to catch
if this occurs.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926054305.2671436-6-npiggin@gmail.com

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

@@ -2794,6 +2794,16 @@ masked_Hinterrupt:
 masked_interrupt:
 	.endif
 	stw	r9,PACA_EXGEN+EX_CCR(r13)
+#ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
+	/*
+	 * Ensure there was no previous MUST_HARD_MASK interrupt or
+	 * HARD_DIS setting.
+	 */
+	lbz	r9,PACAIRQHAPPENED(r13)
+	andi.	r9,r9,(PACA_IRQ_MUST_HARD_MASK|PACA_IRQ_HARD_DIS)
+0:	tdnei	r9,0
+	EMIT_BUG_ENTRY 0b,__FILE__,__LINE__,0
+#endif
 	lbz	r9,PACAIRQHAPPENED(r13)
 	or	r9,r9,r10
 	stb	r9,PACAIRQHAPPENED(r13)