diff mbox series

[b:azure-4.15,f:azure,1/2] hv_utils: return error if host timesysnc update is stale

Message ID 20201216001223.463961-2-kelsey.skunberg@canonical.com
State New
Headers show
Series Keep Chrony time in sync | expand

Commit Message

Kelsey Skunberg Dec. 16, 2020, 12:12 a.m. UTC
From: Vineeth Pillai <viremana@linux.microsoft.com>

BugLink: https://bugs.launchpad.net/bugs/1896784

If for any reason, host timesync messages were not processed by
the guest, hv_ptp_gettime() returns a stale value and the
caller (clock_gettime, PTP ioctl etc) has no means to know this
now. Return an error so that the caller knows about this.

Signed-off-by: Vineeth Pillai <viremana@linux.microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20200821152523.99364-1-viremana@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
(backported from commit 90b125f4cd2697f949f5877df723a0b710693dd0)
[KelseyS: context change]
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>
---
 drivers/hv/hv_util.c | 46 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 11 deletions(-)
diff mbox series

Patch

diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
index ca4c85672cc1..a395f50b3ca2 100644
--- a/drivers/hv/hv_util.c
+++ b/drivers/hv/hv_util.c
@@ -282,26 +282,52 @@  static struct {
 	spinlock_t			lock;
 } host_ts;
 
-static struct timespec64 hv_get_adj_host_time(void)
+static inline u64 reftime_to_ns(u64 reftime)
 {
-	struct timespec64 ts;
-	u64 newtime, reftime;
+	return (reftime - WLTIMEDELTA) * 100;
+}
+
+/*
+ * Hard coded threshold for host timesync delay: 600 seconds
+ */
+static const u64 HOST_TIMESYNC_DELAY_THRESH = 600 * (u64)NSEC_PER_SEC;
+
+static int hv_get_adj_host_time(struct timespec64 *ts)
+{
+	u64 newtime, reftime, timediff_adj;
 	unsigned long flags;
+	int ret = 0;
 
 	spin_lock_irqsave(&host_ts.lock, flags);
 	reftime = hyperv_cs->read(hyperv_cs);
-	newtime = host_ts.host_time + (reftime - host_ts.ref_time);
-	ts = ns_to_timespec64((newtime - WLTIMEDELTA) * 100);
+
+	/*
+	 * We need to let the caller know that last update from host
+	 * is older than the max allowable threshold. clock_gettime()
+	 * and PTP ioctl do not have a documented error that we could
+	 * return for this specific case. Use ESTALE to report this.
+	 */
+	timediff_adj = reftime - host_ts.ref_time;
+	if (timediff_adj * 100 > HOST_TIMESYNC_DELAY_THRESH) {
+		pr_warn_once("TIMESYNC IC: Stale time stamp, %llu nsecs old\n",
+			     (timediff_adj * 100));
+		ret = -ESTALE;
+	}
+
+	newtime = host_ts.host_time + timediff_adj;
+	*ts = ns_to_timespec64(reftime_to_ns(newtime));
 	spin_unlock_irqrestore(&host_ts.lock, flags);
 
-	return ts;
+	return ret;
 }
 
 static void hv_set_host_time(struct work_struct *work)
 {
-	struct timespec64 ts = hv_get_adj_host_time();
 
-	do_settimeofday64(&ts);
+	struct timespec64 ts;
+
+	if (!hv_get_adj_host_time(&ts))
+		do_settimeofday64(&ts);
 }
 
 /*
@@ -621,9 +647,7 @@  static int hv_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
 
 static int hv_ptp_gettime(struct ptp_clock_info *info, struct timespec64 *ts)
 {
-	*ts = hv_get_adj_host_time();
-
-	return 0;
+	return hv_get_adj_host_time(ts);
 }
 
 static struct ptp_clock_info ptp_hyperv_info = {