PTP: add kvm PTP driver

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
===============================================================================

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.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

drivers/ptp/Kconfig

@@ -90,4 +90,16 @@ config PTP_1588_CLOCK_PCH
 	  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 && X86
+	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

drivers/ptp/Makefile

@@ -6,3 +6,4 @@ ptp-y					:= ptp_clock.o ptp_chardev.o ptp_sysfs.o
 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

drivers/ptp/ptp_kvm.c

@@ -0,0 +1,200 @@
+/*
+ * 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 <asm/kvmclock.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;
+
+static struct kvm_clock_pairing clock_pair;
+static phys_addr_t clock_pair_gpa;
+
+static int ptp_kvm_get_time_fn(ktime_t *device_time,
+			       struct system_counterval_t *system_counter,
+			       void *ctx)
+{
+	unsigned long ret;
+	struct timespec64 tspec;
+	unsigned version;
+	int cpu;
+	struct pvclock_vcpu_time_info *src;
+
+	spin_lock(&kvm_ptp_lock);
+
+	preempt_disable_notrace();
+	cpu = smp_processor_id();
+	src = &hv_clock[cpu].pvti;
+
+	do {
+		/*
+		 * We are using a TSC value read in the hosts
+		 * kvm_hc_clock_pairing handling.
+		 * So any changes to tsc_to_system_mul
+		 * and tsc_shift or any other pvclock
+		 * data invalidate that measurement.
+		 */
+		version = pvclock_read_begin(src);
+
+		ret = kvm_hypercall2(KVM_HC_CLOCK_PAIRING,
+				     clock_pair_gpa,
+				     KVM_CLOCK_PAIRING_WALLCLOCK);
+		if (ret != 0) {
+			pr_err_ratelimited("clock pairing hypercall ret %lu\n", ret);
+			spin_unlock(&kvm_ptp_lock);
+			preempt_enable_notrace();
+			return -EOPNOTSUPP;
+		}
+
+		tspec.tv_sec = clock_pair.sec;
+		tspec.tv_nsec = clock_pair.nsec;
+		ret = __pvclock_read_cycles(src, clock_pair.tsc);
+	} while (pvclock_read_retry(src, version));
+
+	preempt_enable_notrace();
+
+	system_counter->cycles = ret;
+	system_counter->cs = &kvm_clock;
+
+	*device_time = timespec64_to_ktime(tspec);
+
+	spin_unlock(&kvm_ptp_lock);
+
+	return 0;
+}
+
+static int ptp_kvm_getcrosststamp(struct ptp_clock_info *ptp,
+				  struct system_device_crosststamp *xtstamp)
+{
+	return get_device_system_crosststamp(ptp_kvm_get_time_fn, NULL,
+					     NULL, xtstamp);
+}
+
+/*
+ * 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 int ptp_kvm_settime(struct ptp_clock_info *ptp,
+			   const struct timespec64 *ts)
+{
+	return -EOPNOTSUPP;
+}
+
+static int ptp_kvm_gettime(struct ptp_clock_info *ptp, struct timespec64 *ts)
+{
+	unsigned long ret;
+	struct timespec64 tspec;
+
+	spin_lock(&kvm_ptp_lock);
+
+	ret = kvm_hypercall2(KVM_HC_CLOCK_PAIRING,
+			     clock_pair_gpa,
+			     KVM_CLOCK_PAIRING_WALLCLOCK);
+	if (ret != 0) {
+		pr_err_ratelimited("clock offset hypercall ret %lu\n", ret);
+		spin_unlock(&kvm_ptp_lock);
+		return -EOPNOTSUPP;
+	}
+
+	tspec.tv_sec = clock_pair.sec;
+	tspec.tv_nsec = clock_pair.nsec;
+	spin_unlock(&kvm_ptp_lock);
+
+	memcpy(ts, &tspec, sizeof(struct timespec64));
+
+	return 0;
+}
+
+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,
+	.getcrosststamp = ptp_kvm_getcrosststamp,
+};
+
+/* 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)
+{
+	clock_pair_gpa = slow_virt_to_phys(&clock_pair);
+	hv_clock = pvclock_pvti_cpu0_va();
+
+	if (!hv_clock)
+		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);
+
+	return 0;
+}
+
+module_init(ptp_kvm_init);
+module_exit(ptp_kvm_exit);
+
+MODULE_AUTHOR("Marcelo Tosatti <mtosatti@redhat.com>");
+MODULE_DESCRIPTION("PTP clock using KVMCLOCK");
+MODULE_LICENSE("GPL");