[patch 1/4] KVM: x86: provide realtime host clock via vsyscall notifiers

[Marcelo Tosatti <mtosatti@redhat.com>]

[-- Attachment #1: kvm-do-realtime --]
[-- Type: text/plain, Size: 2010 bytes --]

Expose the realtime host clock and save the TSC value
used for the clock calculation.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

---
 arch/x86/kvm/x86.c |   36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

v2: unify nsec_base (Radim)

Index: kvm-ptpdriver/arch/x86/kvm/x86.c
===================================================================
--- kvm-ptpdriver.orig/arch/x86/kvm/x86.c	2017-01-13 16:43:15.013244682 -0200
+++ kvm-ptpdriver/arch/x86/kvm/x86.c	2017-01-20 09:56:41.404534904 -0200
@@ -1139,6 +1139,7 @@
 
 	u64		boot_ns;
 	u64		nsec_base;
+	u64		wall_time_sec;
 };
 
 static struct pvclock_gtod_data pvclock_gtod_data;
@@ -1162,6 +1163,8 @@
 	vdata->boot_ns			= boot_ns;
 	vdata->nsec_base		= tk->tkr_mono.xtime_nsec;
 
+	vdata->wall_time_sec            = tk->xtime_sec;
+
 	write_seqcount_end(&vdata->seq);
 }
 #endif
@@ -1623,6 +1626,28 @@
 	return mode;
 }
 
+static int do_realtime(struct timespec *ts, cycle_t *cycle_now)
+{
+	struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
+	unsigned long seq;
+	int mode;
+	u64 ns;
+
+	do {
+		seq = read_seqcount_begin(&gtod->seq);
+		mode = gtod->clock.vclock_mode;
+		ts->tv_sec = gtod->wall_time_sec;
+		ns = gtod->nsec_base;
+		ns += vgettsc(cycle_now);
+		ns >>= gtod->clock.shift;
+	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
+
+	ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
+	ts->tv_nsec = ns;
+
+	return mode;
+}
+
 /* returns true if host is using tsc clocksource */
 static bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now)
 {
@@ -1632,6 +1657,17 @@
 
 	return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;
 }
+
+/* returns true if host is using tsc clocksource */
+static bool kvm_get_walltime_and_clockread(struct timespec *ts,
+					   cycle_t *cycle_now)
+{
+	/* checked again under seqlock below */
+	if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
+		return false;
+
+	return do_realtime(ts, cycle_now) == VCLOCK_TSC;
+}
 #endif
 
 /*