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authorJanakarajan Natarajan <Janakarajan.Natarajan@amd.com>2017-04-25 16:44:03 -0500
committerThomas Gleixner <tglx@linutronix.de>2017-04-30 13:35:11 +0200
commit88d879d29f9cc0de2d930b584285638cdada6625 (patch)
parenta5859c6d7b6114fc0e52be40f7b0f5451c4aba93 (diff)
Prevent timer value 0 for MWAITX
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>
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
index a8e91ae89fb3..29df077cb089 100644
--- a/arch/x86/lib/delay.c
+++ b/arch/x86/lib/delay.c
@@ -93,6 +93,13 @@ static void delay_mwaitx(unsigned long __loops)
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 (;;) {