[tip: x86/misc] x86/nmi: Fix nmi_handle() duration miscalculation

[tip-bot2 for Libing Zhou]

The following commit has been merged into the x86/misc branch of tip:

Commit-ID:     f94c91f7ba3ba7de2bc8aa31be28e1abb22f849e
Gitweb:        https://git.kernel.org/tip/f94c91f7ba3ba7de2bc8aa31be28e1abb22f849e
Author:        Libing Zhou <libing.zhou@xxxxxxxxxxxxxxx>
AuthorDate:    Thu, 20 Aug 2020 10:56:41 +08:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Thu, 01 Oct 2020 14:42:08 +02:00

x86/nmi: Fix nmi_handle() duration miscalculation

When nmi_check_duration() is checking the time an NMI handler took to
execute, the whole_msecs value used should be read from the @duration
argument, not from the ->max_duration, the latter being used to store
the current maximal duration.

 [ bp: Rewrite commit message. ]

Fixes: 248ed51048c4 ("x86/nmi: Remove irq_work from the long duration NMI handler")
Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Libing Zhou <libing.zhou@xxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Changbin Du <changbin.du@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20200820025641.44075-1-libing.zhou@xxxxxxxxxxxxxxx
---
 arch/x86/kernel/nmi.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 4fc9954..4738166 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -102,7 +102,6 @@ fs_initcall(nmi_warning_debugfs);
 
 static void nmi_check_duration(struct nmiaction *action, u64 duration)
 {
-	u64 whole_msecs = READ_ONCE(action->max_duration);
 	int remainder_ns, decimal_msecs;
 
 	if (duration < nmi_longest_ns || duration < action->max_duration)
@@ -110,12 +109,12 @@ static void nmi_check_duration(struct nmiaction *action, u64 duration)
 
 	action->max_duration = duration;
 
-	remainder_ns = do_div(whole_msecs, (1000 * 1000));
+	remainder_ns = do_div(duration, (1000 * 1000));
 	decimal_msecs = remainder_ns / 1000;
 
 	printk_ratelimited(KERN_INFO
 		"INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",
-		action->handler, whole_msecs, decimal_msecs);
+		action->handler, duration, decimal_msecs);
 }
 
 static int nmi_handle(unsigned int type, struct pt_regs *regs)