Patch "Prevent timer value 0 for MWAITX" has been added to the 4.4-stable tree

Patch "Prevent timer value 0 for MWAITX" has been added to the 4.4-stable tree

[gregkh]

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

    Prevent timer value 0 for MWAITX

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:
     prevent-timer-value-0-for-mwaitx.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 <stable@vger.kernel.org> know about it.


>From 88d879d29f9cc0de2d930b584285638cdada6625 Mon Sep 17 00:00:00 2001
From: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
Date: Tue, 25 Apr 2017 16:44:03 -0500
Subject: Prevent timer value 0 for MWAITX

From: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>

commit 88d879d29f9cc0de2d930b584285638cdada6625 upstream.

Newer hardware has uncovered a bug in the software implementation of
using MWAITX for the delay function. A value of 0 for the timer is meant
to indicate that a timeout will not be used to exit MWAITX. On newer
hardware this can result in MWAITX never returning, resulting in NMI
soft lockup messages being printed. On older hardware, some of the other
conditions under which MWAITX can exit masked this issue. The AMD APM
does not currently document this and will be updated.

Please refer to http://marc.info/?l=kvm&m=148950623231140 for
information regarding NMI soft lockup messages on an AMD Ryzen 1800X.
This has been root-caused as a 0 passed to MWAITX causing it to wait
indefinitely.

This change has the added benefit of avoiding the unnecessary setup of
MONITORX/MWAITX when the delay value is zero.

Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
Link: http://lkml.kernel.org/r/1493156643-29366-1-git-send-email-Janakarajan.Natarajan@amd.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/lib/delay.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/arch/x86/lib/delay.c
+++ b/arch/x86/lib/delay.c
@@ -93,6 +93,13 @@ static void delay_mwaitx(unsigned long _
 {
 	u64 start, end, delay, loops = __loops;
 
+	/*
+	 * Timer value of 0 causes MWAITX to wait indefinitely, unless there
+	 * is a store on the memory monitored by MONITORX.
+	 */
+	if (loops == 0)
+		return;
+
 	start = rdtsc_ordered();
 
 	for (;;) {


Patches currently in stable-queue which might be from Janakarajan.Natarajan@amd.com are

queue-4.4/prevent-timer-value-0-for-mwaitx.patch