Revert "powerpc/64s/interrupt: Don't enable MSR[EE] in irq handlers unless perf is in use"

This reverts commit 0faf20a.

This made all our ppc64le builds hard lockup / hang. Reported upstream.

Link: https://lore.kernel.org/linuxppc-dev/CANiq72n_FmDx=r-o9J8gYc6LpwRL5EGmhM6Xzwv27Xc7h1TNDw@mail.gmail.com/
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

arch/powerpc/include/asm/hw_irq.h

@@ -345,54 +345,17 @@ static inline bool lazy_irq_pending_nocheck(void)
 bool power_pmu_wants_prompt_pmi(void);
 
 /*
- * This is called by asynchronous interrupts to check whether to
- * conditionally re-enable hard interrupts after having cleared
- * the source of the interrupt. They are kept disabled if there
- * is a different soft-masked interrupt pending that requires hard
- * masking.
+ * This is called by asynchronous interrupts to conditionally
+ * re-enable hard interrupts after having cleared the source
+ * of the interrupt. They are kept disabled if there is a different
+ * soft-masked interrupt pending that requires hard masking.
  */
-static inline bool should_hard_irq_enable(void)
+static inline void may_hard_irq_enable(void)
 {
-#ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
-	WARN_ON(irq_soft_mask_return() == IRQS_ENABLED);
-	WARN_ON(mfmsr() & MSR_EE);
-#endif
-#ifdef CONFIG_PERF_EVENTS
-	/*
-	 * If the PMU is not running, there is not much reason to enable
-	 * MSR[EE] in irq handlers because any interrupts would just be
-	 * soft-masked.
-	 *
-	 * TODO: Add test for 64e
-	 */
-	if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && !power_pmu_wants_prompt_pmi())
-		return false;
-
-	if (get_paca()->irq_happened & PACA_IRQ_MUST_HARD_MASK)
-		return false;
-
-	return true;
-#else
-	return false;
-#endif
-}
-
-/*
- * Do the hard enabling, only call this if should_hard_irq_enable is true.
- */
-static inline void do_hard_irq_enable(void)
-{
-#ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
-	WARN_ON(irq_soft_mask_return() == IRQS_ENABLED);
-	WARN_ON(get_paca()->irq_happened & PACA_IRQ_MUST_HARD_MASK);
-	WARN_ON(mfmsr() & MSR_EE);
-#endif
-	/*
-	 * This allows PMI interrupts (and watchdog soft-NMIs) through.
-	 * There is no other reason to enable this way.
-	 */
-	get_paca()->irq_happened &= ~PACA_IRQ_HARD_DIS;
-	__hard_irq_enable();
+	if (!(get_paca()->irq_happened & PACA_IRQ_MUST_HARD_MASK)) {
+		get_paca()->irq_happened &= ~PACA_IRQ_HARD_DIS;
+		__hard_irq_enable();
+	}
 }
 
 static inline bool arch_irq_disabled_regs(struct pt_regs *regs)
@@ -473,7 +436,7 @@ static inline bool arch_irq_disabled_regs(struct pt_regs *regs)
 	return !(regs->msr & MSR_EE);
 }
 
-static inline bool should_hard_irq_enable(void)
+static inline bool may_hard_irq_enable(void)
 {
 	return false;
 }

arch/powerpc/kernel/dbell.c

@@ -27,8 +27,7 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(doorbell_exception)
 
 	ppc_msgsync();
 
-	if (should_hard_irq_enable())
-		do_hard_irq_enable();
+	may_hard_irq_enable();
 
 	kvmppc_clear_host_ipi(smp_processor_id());
 	__this_cpu_inc(irq_stat.doorbell_irqs);

arch/powerpc/kernel/irq.c

@@ -745,8 +745,7 @@ void __do_irq(struct pt_regs *regs)
 	irq = ppc_md.get_irq();
 
 	/* We can hard enable interrupts now to allow perf interrupts */
-	if (should_hard_irq_enable())
-		do_hard_irq_enable();
+	may_hard_irq_enable();
 
 	/* And finally process it */
 	if (unlikely(!irq))

arch/powerpc/kernel/time.c

@@ -609,23 +609,22 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(timer_interrupt)
 		return;
 	}
 
-	/* Conditionally hard-enable interrupts. */
-	if (should_hard_irq_enable()) {
-		/*
-		 * Ensure a positive value is written to the decrementer, or
-		 * else some CPUs will continue to take decrementer exceptions.
-		 * When the PPC_WATCHDOG (decrementer based) is configured,
-		 * keep this at most 31 bits, which is about 4 seconds on most
-		 * systems, which gives the watchdog a chance of catching timer
-		 * interrupt hard lockups.
-		 */
-		if (IS_ENABLED(CONFIG_PPC_WATCHDOG))
-			set_dec(0x7fffffff);
-		else
-			set_dec(decrementer_max);
+	/* Ensure a positive value is written to the decrementer, or else
+	 * some CPUs will continue to take decrementer exceptions. When the
+	 * PPC_WATCHDOG (decrementer based) is configured, keep this at most
+	 * 31 bits, which is about 4 seconds on most systems, which gives
+	 * the watchdog a chance of catching timer interrupt hard lockups.
+	 */
+	if (IS_ENABLED(CONFIG_PPC_WATCHDOG))
+		set_dec(0x7fffffff);
+	else
+		set_dec(decrementer_max);
+
+	/* Conditionally hard-enable interrupts now that the DEC has been
+	 * bumped to its maximum value
+	 */
+	may_hard_irq_enable();
 
-		do_hard_irq_enable();
-	}
 
 #if defined(CONFIG_PPC32) && defined(CONFIG_PPC_PMAC)
 	if (atomic_read(&ppc_n_lost_interrupts) != 0)