xen/arm: set the system time in Xen via the XENPF_settime64 hypercall

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 <stefano.stabellini@eu.citrix.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 48 insertions, 0 deletions

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 6370222b8053..75cd7345c654 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -26,7 +26,10 @@
 #include <linux/cpufreq.h>
 #include <linux/cpu.h>
 #include <linux/console.h>
+#include <linux/pvclock_gtod.h>
+#include <linux/time64.h>
 #include <linux/timekeeping.h>
+#include <linux/timekeeper_internal.h>
 
 #include <linux/mm.h>
 
@@ -115,6 +118,49 @@ static void xen_read_wallclock(struct timespec64 *ts)
         *ts = timespec64_add(now, ts_monotonic);
 }
 
+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, system_time;
+        struct timekeeper *tk = priv;
+
+        now.tv_sec = tk->xtime_sec;
+        now.tv_nsec = (long)(tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift);
+        system_time = timespec64_add(now, tk->wall_to_monotonic);
+
+        /*
+         * 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.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 = timespec64_to_ns(&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;
@@ -311,6 +357,8 @@ static int __init xen_guest_init(void)
 
         pv_time_ops.steal_clock = xen_stolen_accounting;
         static_key_slow_inc(&paravirt_steal_enabled);
+        if (xen_initial_domain())
+                pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier);
 
         return 0;
 }