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

Marcelo Tosatti
2017-01-13T12:09:27Z

[-- Attachment #1: kvm-ptpdriver --]
[-- Type: text/plain, Size: 6517 bytes --]

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@redhat.com>");
+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