Re: [PATCH 1/6] irq_work: Re-raise pending irq_work after system resume

[Adrian Hunter <adrian.hunter@intel.com>]

On 02/11/2026 18:39, Sebastian Andrzej Siewior wrote:
> On 2026-11-02 12:54:22 [+0200], Adrian Hunter wrote:
>>
>> Yes CPUs remain online for suspend2idle, but currently the choice between
>> suspend2idle and "deep" (S3) suspend is a user space choice,
>> refer /sys/power/mem_sleep.  Many modern systems do not support S3
>> anymore, but it has not gone away.
>>
>>>
>>> Anyway, I'm torn; I would much rather make this trigger a WARN and have
>>
>> AI now also identifies ftrace, BPF, GHES NMI, and #MC as possible causes,
>> not just perf.  I haven't tried to confirm any of those.
>>
>> And, belatedly, AI is now saying an irq_work raised before lapic_resume()
>> might result in #GP if the APIC is left in xAPIC mode at resume.  Also
>> not confirmed.
> 
> Could we flush this before similarly to what happens during CPU-hotplug.
> The question is if this event can stay enqueued during suspend (and
> handled on resume) or should be taken care before entering suspend.

WRT "might result in #GP if the APIC is left in xAPIC mode at resume",
the systems I have checked restore the APIC in x2APIC mode, so the
issue is theoretical at this point, although I can get "unchecked MSR
access error: WRMSR to 0x83f" if I deliberately add code to change
x2APIC to xAPIC early in S3 wake (in x86_acpi_suspend_lowlevel()),
and then do:

  perf record -e power:suspend_resume --filter 'action == "machine_suspend" && start == 0' --no-buffering -C 0 -o /tmp/x.data &
  rtcwake -m mem -s 10

The error can be avoided with:

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 08c9aa176c33..41f93586f22c 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -63,6 +63,7 @@ extern int apic_verbosity;
 extern int local_apic_timer_c2_ok;
 
 extern bool apic_is_disabled;
+extern bool lapic_suspended;
 extern unsigned int lapic_timer_period;
 
 extern enum apic_intr_mode_id apic_intr_mode;
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 40fa7bc7fb97..187cbfad0d76 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2385,6 +2385,8 @@ void __init up_late_init(void)
 }
 #endif
 
+bool lapic_suspended;
+
 /*
  * Power management
  */
@@ -2454,6 +2456,8 @@ static int lapic_suspend(void *data)
 	 */
 	mask_ioapic_entries();
 
+	WRITE_ONCE(lapic_suspended, true);
+
 	disable_local_APIC();
 
 	irq_remapping_disable();
@@ -2534,6 +2538,8 @@ static void lapic_resume(void *data)
 
 	irq_remapping_reenable(x2apic_mode);
 
+	WRITE_ONCE(lapic_suspended, false);
+
 	local_irq_restore(flags);
 }
 
diff --git a/arch/x86/kernel/irq_work.c b/arch/x86/kernel/irq_work.c
index 308c62411ff4..32386b7cf84e 100644
--- a/arch/x86/kernel/irq_work.c
+++ b/arch/x86/kernel/irq_work.c
@@ -25,7 +25,7 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_irq_work)
 
 void arch_irq_work_raise(void)
 {
-	if (!arch_irq_work_has_interrupt())
+	if (!arch_irq_work_has_interrupt() || READ_ONCE(lapic_suspended))
 		return;
 
 	__apic_send_IPI_self(IRQ_WORK_VECTOR);