From: Peter Martincic <pmartincic@microsoft.com>

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: Peter Martincic <pmartincic@microsoft.com>
---
 drivers/hv/hv_util.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
index 42aec2c5606a..9c97c4065fe7 100644
--- a/drivers/hv/hv_util.c
+++ b/drivers/hv/hv_util.c
@@ -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);
 }
 
-- 
2.34.1

On Mon, Nov 27, 2023 at 01:35:24PM -0800, pmartincic@linux.microsoft.com wrote:
> From: Peter Martincic <pmartincic@microsoft.com>
> 
> 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: Peter Martincic <pmartincic@microsoft.com>

Looks good to me.

Acked-by: Boqun Feng <boqun.feng@gmail.com>

Regards,
Boqun

> ---
>  drivers/hv/hv_util.c | 31 ++++++++++++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
> index 42aec2c5606a..9c97c4065fe7 100644
> --- a/drivers/hv/hv_util.c
> +++ b/drivers/hv/hv_util.c
> @@ -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);
>  }
>  
> -- 
> 2.34.1
>

On Thu, Nov 30, 2023 at 11:16:43AM -0800, Boqun Feng wrote:
> On Mon, Nov 27, 2023 at 01:35:24PM -0800, pmartincic@linux.microsoft.com wrote:
> > From: Peter Martincic <pmartincic@microsoft.com>
> > 
> > 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: Peter Martincic <pmartincic@microsoft.com>
> 
> Looks good to me.
> 
> Acked-by: Boqun Feng <boqun.feng@gmail.com>

Applied to hyperv-fixes, thanks!