x86/apic: Mask IOAPIC entries when disabling the local APIC

When a system suspends, the local APIC is disabled in the suspend sequence,
but the IOAPIC is left in the current state. This means unmasked interrupt
lines stay unmasked. This is usually the case for IOAPIC pin 9 to which the
ACPI interrupt is connected.

That means that in suspended state the IOAPIC can respond to an external
interrupt, e.g. the wakeup via keyboard/RTC/ACPI, but the interrupt message
cannot be handled by the disabled local APIC. As a consequence the Remote
IRR bit is set, but the local APIC does not send an EOI to acknowledge
it. This causes the affected interrupt line to become stale and the stale
Remote IRR bit will cause a hang when __synchronize_hardirq() is invoked
for that interrupt line.

To prevent this, mask all IOAPIC entries before disabling the local
APIC. The resume code already has the unmask operation inside.

[ tglx: Massaged changelog ]

Signed-off-by: Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/1579076539-7267-1-git-send-email-TonyWWang-oc@zhaoxin.com

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 4b0f9117e1cd8ce68f1f7514e5f8584f327f23a2..5f973fed3c9ff21ba96692cd6d6c1d454c16acf4 100644 (file)
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2639,6 +2639,13 @@ static int lapic_suspend(void)
 #endif
 
        local_irq_save(flags);
+
+       /*
+        * Mask IOAPIC before disabling the local APIC to prevent stale IRR
+        * entries on some implementations.
+        */
+       mask_ioapic_entries();
+
        disable_local_APIC();
 
        irq_remapping_disable();