[PATCH] virt: vboxguest: send the heartbeat at the interval

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Josef Bacik <josef@toxicpanda.com>

The host tells the guest how often it expects a heartbeat.
vbg_heartbeat_timer() re-arms its timer with

  mod_timer(&gdev->heartbeat_timer, msecs_to_jiffies(interval));

But the second argument of mod_timer() is a point in time, not a delay.
An interval, taken as a point in time, lies in the past, so the timer
expires again on the next tick.  Whatever the host has asked for, the
guest sends a heartbeat 100 to 1000 times a second, depending on HZ, and
each of them is a request to the host, that is a VM exit from the timer
softirq.

On 32 bit, where jiffies starts five minutes before it wraps around,
these small values lie in the future at first.  That also goes for the 0
with which vbg_heartbeat_init() means to start the timer at once: if the
driver is loaded during boot, the first heartbeat is only sent five
minutes after boot.

Add jiffies in both places.  Every VirtualBox guest now sends its
heartbeat at the interval which the host has asked for.

Fixes: 0ba002bc4393 ("virt: Add vboxguest driver for Virtual Box Guest integration")
Cc: stable <stable@kernel.org>
Cc: Hans de Goede <hansg@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/virt/vboxguest/vboxguest_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/virt/vboxguest/vboxguest_core.c b/drivers/virt/vboxguest/vboxguest_core.c
index b5dc0d01facd..be6a8cc4e712 100644
--- a/drivers/virt/vboxguest/vboxguest_core.c
+++ b/drivers/virt/vboxguest/vboxguest_core.c
@@ -422,7 +422,7 @@ static void vbg_heartbeat_timer(struct timer_list *t)
 
 	vbg_req_perform(gdev, gdev->guest_heartbeat_req);
 	mod_timer(&gdev->heartbeat_timer,
-		  msecs_to_jiffies(gdev->heartbeat_interval_ms));
+		  jiffies + msecs_to_jiffies(gdev->heartbeat_interval_ms));
 }
 
 /**
@@ -482,7 +482,7 @@ static int vbg_heartbeat_init(struct vbg_dev *gdev)
 
 	vbg_info("%s: Setting up heartbeat to trigger every %d milliseconds\n",
 		 __func__, gdev->heartbeat_interval_ms);
-	mod_timer(&gdev->heartbeat_timer, 0);
+	mod_timer(&gdev->heartbeat_timer, jiffies);
 
 	return 0;
 }
-- 
2.56.0