Patch "ACPI / APEI: Fix NMI notification handling" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ACPI / APEI: Fix NMI notification handling

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
acpi-apei-fix-nmi-notification-handling.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Prarit Bhargava <[email protected]>
Date: Wed, 30 Nov 2016 08:19:39 -0500
Subject: ACPI / APEI: Fix NMI notification handling

From: Prarit Bhargava <[email protected]>

commit a545715d2dae8d071c5b06af947b07ffa846b288 upstream.

When removing and adding cpu 0 on a system with GHES NMI the following stack trace is seen when re-adding the cpu:

WARNING: CPU: 0 PID: 0 at arch/x86/kernel/apic/apic.c:1349 setup_local_APIC+
Modules linked in: nfsv3 rpcsec_gss_krb5 nfsv4 nfs fscache coretemp intel_ra
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.9.0-rc6+ #2
Call Trace:
 dump_stack+0x63/0x8e
 __warn+0xd1/0xf0
 warn_slowpath_null+0x1d/0x20
 setup_local_APIC+0x275/0x370
 apic_ap_setup+0xe/0x20
 start_secondary+0x48/0x180
 set_init_arg+0x55/0x55
 early_idt_handler_array+0x120/0x120
 x86_64_start_reservations+0x2a/0x2c
 x86_64_start_kernel+0x13d/0x14c

During the cpu bringup, wakeup_cpu_via_init_nmi() is called and issues an NMI on CPU 0. The GHES NMI handler, ghes_notify_nmi() runs the ghes_proc_irq_work work queue which ends up setting IRQ_WORK_VECTOR (0xf6). The "faulty" IR line set at arch/x86/kernel/apic/apic.c:1349 is also 0xf6 (specifically APIC IRR for irqs 255 to 224 is 0x400000) which confirms that something has set the IRQ_WORK_VECTOR line prior to the APIC being initialized.

Commit 2383844d4850 ("GHES: Elliminate double-loop in the NMI handler") incorrectly modified the behavior such that the handler returns NMI_HANDLED only if an error was processed, and incorrectly runs the ghes work queue for every NMI.

This patch modifies the ghes_proc_irq_work() to run as it did prior to 2383844d4850 ("GHES: Elliminate double-loop in the NMI handler") by properly returning NMI_HANDLED and only calling the work queue if NMI_HANDLED has been set.

---
 drivers/acpi/apei/ghes.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

@@ -847,6 +847,8 @@ static int ghes_notify_nmi(unsigned int
 		if (ghes_read_estatus(ghes, 1)) {
 			ghes_clear_estatus(ghes);
 			continue;
+		} else {
+			ret = NMI_HANDLED;
 		}
 
 		sev = ghes_severity(ghes->estatus->error_severity);

@@ -858,12 +860,11 @@ static int ghes_notify_nmi(unsigned int
 
 		__process_error(ghes);
 		ghes_clear_estatus(ghes);
-
-		ret = NMI_HANDLED;
 	}
 
 #ifdef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
-	irq_work_queue(&ghes_proc_irq_work);
+	if (ret == NMI_HANDLED)
+		irq_work_queue(&ghes_proc_irq_work);
 #endif
 	atomic_dec(&ghes_in_nmi);
 	return ret;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/acpi-apei-fix-nmi-notification-handling.patch