[v2,7/7] xen/arm: set the system time in Xen via the XENPF_settime64 hypercall

Commit Message

Stefano Stabellini Nov. 10, 2015, 11:57 a.m. UTC

If Linux is running as dom0, call XENPF_settime64 to update the system
time in Xen on pvclock_gtod notifications.

Signed-off-by: Stefano Stabellini <[e-mail]>

---

Changes in v2:
- properly convert arch_timer ticker to nsec
- rename dom0_op to platform_op
- use timespec64 interfaces
- use XENPF_settime64
---
 arch/arm/xen/enlighten.c |   54 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

Comments

Arnd Bergmann Nov. 10, 2015, 12:39 p.m. UTC | #1

On Tuesday 10 November 2015 11:57:55 Stefano Stabellini wrote:
> +       op.u.settime64.nsecs = now.tv_nsec;
> +       op.u.settime64.system_time = arch_timer_read_counter() * (u64)NSEC_PER_SEC;
> +       do_div(op.u.settime64.system_time, arch_timer_get_rate());

NSEC_PER_SEC is a large number, doesn't that multiplication overflow the
64-bit system_time variable?

> +       printk("GTOD: Setting to %llu.%u at %llu\n",

				   %llu.%09u

so you get the leading zeroes.

> +              op.u.settime64.secs,
> +              op.u.settime64.nsecs,
> +              op.u.settime64.system_time);
> +       (void)HYPERVISOR_platform_op(&op);

	Arnd

Stefano Stabellini Nov. 10, 2015, 3:58 p.m. UTC | #2

On Tue, 10 Nov 2015, Arnd Bergmann wrote:
> On Tuesday 10 November 2015 11:57:55 Stefano Stabellini wrote:
> > +       op.u.settime64.nsecs = now.tv_nsec;
> > +       op.u.settime64.system_time = arch_timer_read_counter() * (u64)NSEC_PER_SEC;
> > +       do_div(op.u.settime64.system_time, arch_timer_get_rate());
> 
> NSEC_PER_SEC is a large number, doesn't that multiplication overflow the
> 64-bit system_time variable?

It could be a concern, you are right. I think I can solve this issue and
remove multiple do_divs by calculating nsec_per_tick at initialization
time and use it here and in xen_read_wallclock.


> > +       printk("GTOD: Setting to %llu.%u at %llu\n",
> 
> 				   %llu.%09u
> 
> so you get the leading zeroes.
> 
> > +              op.u.settime64.secs,
> > +              op.u.settime64.nsecs,
> > +              op.u.settime64.system_time);
> > +       (void)HYPERVISOR_platform_op(&op);
> 
> 	Arnd
>

Patch

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 32675b5..a991b25 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -28,6 +28,7 @@ 
 #include <linux/cpufreq.h>
 #include <linux/cpu.h>
 #include <linux/console.h>
+#include <linux/pvclock_gtod.h>
 #include <linux/timekeeping.h>
 #include <clocksource/arm_arch_timer.h>
 
@@ -125,6 +126,52 @@  static void xen_read_wallclock(struct timespec64 *ts)
 
 }
 
+static int xen_pvclock_gtod_notify(struct notifier_block *nb,
+				   unsigned long was_set, void *priv)
+{
+	/* Protected by the calling core code serialization */
+	static struct timespec64 next_sync;
+
+	struct xen_platform_op op;
+	struct timespec64 now;
+
+	now = __current_kernel_time64();
+
+	/*
+	 * We only take the expensive HV call when the clock was set
+	 * or when the 11 minutes RTC synchronization time elapsed.
+	 */
+	if (!was_set && timespec64_compare(&now, &next_sync) < 0)
+		return NOTIFY_OK;
+
+	op.interface_version = XENPF_INTERFACE_VERSION;
+	op.cmd = XENPF_settime64;
+	op.u.settime64.mbz = 0;
+	op.u.settime64.secs = now.tv_sec;
+	op.u.settime64.nsecs = now.tv_nsec;
+	op.u.settime64.system_time = arch_timer_read_counter() * (u64)NSEC_PER_SEC;
+	do_div(op.u.settime64.system_time, arch_timer_get_rate());
+	printk("GTOD: Setting to %llu.%u at %llu\n",
+	       op.u.settime64.secs,
+	       op.u.settime64.nsecs,
+	       op.u.settime64.system_time);
+	(void)HYPERVISOR_platform_op(&op);
+
+	/*
+	 * Move the next drift compensation time 11 minutes
+	 * ahead. That's emulating the sync_cmos_clock() update for
+	 * the hardware RTC.
+	 */
+	next_sync = now;
+	next_sync.tv_sec += 11 * 60;
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block xen_pvclock_gtod_notifier = {
+	.notifier_call = xen_pvclock_gtod_notify,
+};
+
 static void xen_percpu_init(void)
 {
 	struct vcpu_register_vcpu_info info;
@@ -323,7 +370,12 @@  static int __init xen_guest_init(void)
 	pv_time_ops.steal_clock = xen_stolen_accounting;
 	static_key_slow_inc(&paravirt_steal_enabled);
 	xen_read_wallclock(&ts);
-	do_settimeofday64(&ts);
+	if (xen_initial_domain())
+		pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier);
+	else {
+		xen_read_wallclock(&ts);
+		do_settimeofday64(&ts);
+	}
 
 	return 0;
 }