[patch 3/3] PTP: add kvm PTP driver

[Marcelo Tosatti]

Add a driver with gettime method returning hosts realtime clock.
This allows Chrony to synchronize host and guest clocks with 
high precision (see results below).

chronyc> sources
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
#* PHC0                          0   3   377     6     +4ns[   +4ns] +/-    3ns

To configure Chronyd to use PHC refclock, add the 
following line to its configuration file:

refclock PHC /dev/ptpX poll 3 dpoll -2 offset 0

Where /dev/ptpX is the kvmclock PTP clock.


---
 drivers/ptp/Kconfig   |   12 +++
 drivers/ptp/Makefile  |    1 
 drivers/ptp/ptp_kvm.c |  180 ++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 193 insertions(+)

Index: kvm-ptpdriver/drivers/ptp/Kconfig
===================================================================
--- kvm-ptpdriver.orig/drivers/ptp/Kconfig	2017-01-13 09:17:31.724568567 -0200
+++ kvm-ptpdriver/drivers/ptp/Kconfig	2017-01-13 09:55:33.344208894 -0200
@@ -90,4 +90,16 @@
 	  To compile this driver as a module, choose M here: the module
 	  will be called ptp_pch.
 
+config PTP_1588_CLOCK_KVM
+	tristate "KVM virtual PTP clock"
+	depends on PTP_1588_CLOCK
+	depends on KVM_GUEST
+	default y
+	help
+	  This driver adds support for using kvm infrastructure as a PTP
+	  clock. This clock is only useful if you are using KVM guests.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called ptp_kvm.
+
 endmenu
Index: kvm-ptpdriver/drivers/ptp/ptp_kvm.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ kvm-ptpdriver/drivers/ptp/ptp_kvm.c	2017-01-13 09:57:55.013440645 -0200
@@ -0,0 +1,180 @@
+/*
+ * Virtual PTP 1588 clock for use with KVM guests
+ *
+ * Copyright (C) 2017 Red Hat Inc.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ */
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <uapi/linux/kvm_para.h>
+#include <asm/kvm_para.h>
+#include <asm/pvclock.h>
+#include <uapi/asm/kvm_para.h>
+
+#include <linux/ptp_clock_kernel.h>
+
+struct kvm_ptp_clock {
+	struct ptp_clock *ptp_clock;
+	struct ptp_clock_info caps;
+};
+
+DEFINE_SPINLOCK(kvm_ptp_lock);
+
+static struct pvclock_vsyscall_time_info *hv_clock;
+
+/*
+ * PTP clock operations
+ */
+
+static int ptp_kvm_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
+{
+	return -EOPNOTSUPP;
+}
+
+static int ptp_kvm_adjtime(struct ptp_clock_info *ptp, s64 delta)
+{
+	return -EOPNOTSUPP;
+}
+
+static struct kvm_clock_offset clock_off;
+static phys_addr_t clock_off_gpa;
+
+static int ptp_kvm_gettime(struct ptp_clock_info *ptp, struct timespec64 *ts)
+{
+	unsigned long ret;
+	struct timespec64 tspec;
+	u64 delta;
+	cycle_t offset;
+	unsigned version;
+	int cpu;
+	struct pvclock_vcpu_time_info *src;
+
+	preempt_disable_notrace();
+	cpu = smp_processor_id();
+	src = &hv_clock[cpu].pvti;
+
+	spin_lock(&kvm_ptp_lock);
+
+	do {
+		/*
+		 * We are measuring the delay between
+		 * kvm_hypercall and rdtsc using TSC,
+		 * and converting that delta to
+		 * tsc_to_system_mul and tsc_shift
+		 * So any changes to tsc_to_system_mul
+		 * and tsc_shift in this region
+		 * invalidate the measurement.
+		 */
+		version = pvclock_read_begin(src);
+
+		ret = kvm_hypercall2(KVM_HC_CLOCK_OFFSET,
+				     clock_off_gpa,
+				     KVM_CLOCK_OFFSET_WALLCLOCK);
+		if (ret != 0) {
+			pr_err("clock offset hypercall ret %lu\n", ret);
+			spin_unlock(&kvm_ptp_lock);
+			preempt_enable_notrace();
+			return -EOPNOTSUPP;
+		}
+
+		tspec.tv_sec = clock_off.sec;
+		tspec.tv_nsec = clock_off.nsec;
+
+		delta = rdtsc_ordered() - clock_off.tsc;
+
+		offset = pvclock_scale_delta(delta, src->tsc_to_system_mul,
+					     src->tsc_shift);
+
+	} while (pvclock_read_retry(src, version));
+
+	preempt_enable_notrace();
+
+	tspec.tv_nsec = tspec.tv_nsec + offset;
+
+	spin_unlock(&kvm_ptp_lock);
+
+	if (tspec.tv_nsec >= NSEC_PER_SEC) {
+		u64 secs = tspec.tv_nsec;
+
+		tspec.tv_nsec = do_div(secs, NSEC_PER_SEC);
+		tspec.tv_sec += secs;
+	}
+
+	memcpy(ts, &tspec, sizeof(struct timespec64));
+
+	return 0;
+}
+
+static int ptp_kvm_settime(struct ptp_clock_info *ptp,
+			   const struct timespec64 *ts)
+{
+	return -EOPNOTSUPP;
+}
+
+static int ptp_kvm_enable(struct ptp_clock_info *ptp,
+			  struct ptp_clock_request *rq, int on)
+{
+	return -EOPNOTSUPP;
+}
+
+static struct ptp_clock_info ptp_kvm_caps = {
+	.owner		= THIS_MODULE,
+	.name		= "KVM virtual PTP",
+	.max_adj	= 0,
+	.n_ext_ts	= 0,
+	.n_pins		= 0,
+	.pps		= 0,
+	.adjfreq	= ptp_kvm_adjfreq,
+	.adjtime	= ptp_kvm_adjtime,
+	.gettime64	= ptp_kvm_gettime,
+	.settime64	= ptp_kvm_settime,
+	.enable		= ptp_kvm_enable,
+};
+
+/* module operations */
+
+static struct kvm_ptp_clock kvm_ptp_clock;
+
+static void __exit ptp_kvm_exit(void)
+{
+	ptp_clock_unregister(kvm_ptp_clock.ptp_clock);
+}
+
+static int __init ptp_kvm_init(void)
+{
+	if (!kvm_para_available())
+		return -ENODEV;
+
+	kvm_ptp_clock.caps = ptp_kvm_caps;
+
+	kvm_ptp_clock.ptp_clock = ptp_clock_register(&kvm_ptp_clock.caps, NULL);
+
+	if (IS_ERR(kvm_ptp_clock.ptp_clock))
+		return PTR_ERR(kvm_ptp_clock.ptp_clock);
+
+	clock_off_gpa = slow_virt_to_phys(&clock_off);
+
+	hv_clock = pvclock_pvti_cpu0_va();
+
+	return 0;
+}
+
+module_init(ptp_kvm_init);
+module_exit(ptp_kvm_exit);
+
+MODULE_AUTHOR("Marcelo Tosatti <mtosatti@xxxxxxxxxx>");
+MODULE_DESCRIPTION("PTP clock using KVMCLOCK");
+MODULE_LICENSE("GPL");
Index: kvm-ptpdriver/drivers/ptp/Makefile
===================================================================
--- kvm-ptpdriver.orig/drivers/ptp/Makefile	2017-01-13 09:17:31.724568567 -0200
+++ kvm-ptpdriver/drivers/ptp/Makefile	2017-01-13 09:17:58.997609570 -0200
@@ -6,3 +6,4 @@
 obj-$(CONFIG_PTP_1588_CLOCK)		+= ptp.o
 obj-$(CONFIG_PTP_1588_CLOCK_IXP46X)	+= ptp_ixp46x.o
 obj-$(CONFIG_PTP_1588_CLOCK_PCH)	+= ptp_pch.o
+obj-$(CONFIG_PTP_1588_CLOCK_KVM)	+= ptp_kvm.o