Commit adf47524 authored by Peter Martincic's avatar Peter Martincic Committed by Wei Liu
Browse files

hv_utils: Allow implicit ICTIMESYNCFLAG_SYNC 



Hyper-V hosts can omit the _SYNC flag to due a bug on resume from modern
suspend. In such a case, the guest may fail to update its time-of-day to
account for the period when it was suspended, and could proceed with a
significantly wrong time-of-day. In such a case when the guest is
significantly behind, fix it by treating a _SAMPLE the same as if _SYNC
was received so that the guest time-of-day is updated.

This is hidden behind param hv_utils.timesync_implicit.

Signed-off-by: default avatarPeter Martincic <pmartincic@microsoft.com>
Acked-by: default avatarBoqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20231127213524.52783-1-pmartincic@linux.microsoft.com


Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
Message-ID: <20231127213524.52783-1-pmartincic@linux.microsoft.com>
parent d206a76d

drivers/hv/hv_util.c

+30 −1
Original line number Diff line number Diff line
@@ -296,6 +296,11 @@ static struct { 
	spinlock_t			lock;

} host_ts;



static bool timesync_implicit;



module_param(timesync_implicit, bool, 0644);

MODULE_PARM_DESC(timesync_implicit, "If set treat SAMPLE as SYNC when clock is behind");



static inline u64 reftime_to_ns(u64 reftime)

{

	return (reftime - WLTIMEDELTA) * 100;
@@ -344,6 +349,29 @@ static void hv_set_host_time(struct work_struct *work) 
		do_settimeofday64(&ts);

}



/*

 * Due to a bug on Hyper-V hosts, the sync flag may not always be sent on resume.

 * Force a sync if the guest is behind.

 */

static inline bool hv_implicit_sync(u64 host_time)

{

	struct timespec64 new_ts;

	struct timespec64 threshold_ts;



	new_ts = ns_to_timespec64(reftime_to_ns(host_time));

	ktime_get_real_ts64(&threshold_ts);



	threshold_ts.tv_sec += 5;



	/*

	 * If guest behind the host by 5 or more seconds.

	 */

	if (timespec64_compare(&new_ts, &threshold_ts) >= 0)

		return true;



	return false;

}



/*

 * Synchronize time with host after reboot, restore, etc.

 *
@@ -384,7 +412,8 @@ static inline void adj_guesttime(u64 hosttime, u64 reftime, u8 adj_flags) 
	spin_unlock_irqrestore(&host_ts.lock, flags);



	/* Schedule work to do do_settimeofday64() */

	if (adj_flags & ICTIMESYNCFLAG_SYNC)

	if ((adj_flags & ICTIMESYNCFLAG_SYNC) ||

	    (timesync_implicit && hv_implicit_sync(host_ts.host_time)))

		schedule_work(&adj_time_work);

}