x86/ioapic: Cleanup the timer_works() irqflags mess

Mark tripped over the creative irqflags handling in the IO-APIC timer
delivery check which ends up doing:

        local_irq_save(flags);
	local_irq_enable();
        local_irq_restore(flags);

which triggered a new consistency check he's working on required for
replacing the POPF based restore with a conditional STI.

That code is a historical mess and none of this is needed. Make it
straightforward use local_irq_disable()/enable() as that's all what is
required. It is invoked from interrupt enabled code nowadays.

Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/87k0tpju47.fsf@nanos.tec.linutronix.de

arch/x86/kernel/apic/io_apic.c

@@ -1620,21 +1620,16 @@ static void __init delay_without_tsc(void)
 static int __init timer_irq_works(void)
 {
 	unsigned long t1 = jiffies;
-	unsigned long flags;
 
 	if (no_timer_check)
 		return 1;
 
-	local_save_flags(flags);
 	local_irq_enable();
-
 	if (boot_cpu_has(X86_FEATURE_TSC))
 		delay_with_tsc();
 	else
 		delay_without_tsc();
 
-	local_irq_restore(flags);
-
 	/*
 	 * Expect a few ticks at least, to be sure some possible
 	 * glue logic does not lock up after one or two first
@@ -1643,10 +1638,10 @@ static int __init timer_irq_works(void)
 	 * least one tick may be lost due to delays.
 	 */
 
-	/* jiffies wrap? */
-	if (time_after(jiffies, t1 + 4))
-		return 1;
-	return 0;
+	local_irq_disable();
+
+	/* Did jiffies advance? */
+	return time_after(jiffies, t1 + 4);
 }
 
 /*
@@ -2163,13 +2158,12 @@ static inline void __init check_timer(void)
 	struct irq_cfg *cfg = irqd_cfg(irq_data);
 	int node = cpu_to_node(0);
 	int apic1, pin1, apic2, pin2;
-	unsigned long flags;
 	int no_pin1 = 0;
 
 	if (!global_clock_event)
 		return;
 
-	local_irq_save(flags);
+	local_irq_disable();
 
 	/*
 	 * get/set the timer IRQ vector:
@@ -2237,7 +2231,6 @@ static inline void __init check_timer(void)
 			goto out;
 		}
 		panic_if_irq_remap("timer doesn't work through Interrupt-remapped IO-APIC");
-		local_irq_disable();
 		clear_IO_APIC_pin(apic1, pin1);
 		if (!no_pin1)
 			apic_printk(APIC_QUIET, KERN_ERR "..MP-BIOS bug: "
@@ -2261,7 +2254,6 @@ static inline void __init check_timer(void)
 		/*
 		 * Cleanup, just in case ...
 		 */
-		local_irq_disable();
 		legacy_pic->mask(0);
 		clear_IO_APIC_pin(apic2, pin2);
 		apic_printk(APIC_QUIET, KERN_INFO "....... failed.\n");
@@ -2278,7 +2270,6 @@ static inline void __init check_timer(void)
 		apic_printk(APIC_QUIET, KERN_INFO "..... works.\n");
 		goto out;
 	}
-	local_irq_disable();
 	legacy_pic->mask(0);
 	apic_write(APIC_LVT0, APIC_LVT_MASKED | APIC_DM_FIXED | cfg->vector);
 	apic_printk(APIC_QUIET, KERN_INFO "..... failed.\n");
@@ -2297,7 +2288,6 @@ static inline void __init check_timer(void)
 		apic_printk(APIC_QUIET, KERN_INFO "..... works.\n");
 		goto out;
 	}
-	local_irq_disable();
 	apic_printk(APIC_QUIET, KERN_INFO "..... failed :(.\n");
 	if (apic_is_x2apic_enabled())
 		apic_printk(APIC_QUIET, KERN_INFO
@@ -2306,7 +2296,7 @@ static inline void __init check_timer(void)
 	panic("IO-APIC + timer doesn't work!  Boot with apic=debug and send a "
 		"report.  Then try booting with the 'noapic' option.\n");
 out:
-	local_irq_restore(flags);
+	local_irq_enable();
 }
 
 /*