[RFC PATCH v9 7/8] ptp: arm64: Enable ptp_kvm for arm64

Jianyong Wu
2019-12-10T03:41:23Z

Currently in arm64 virtualization environment, there is no mechanism to
keep time sync between guest and host. Time in guest will drift compared
with host after boot up as they may both use third party time sources
to correct their time respectively. The time deviation will be in order
of milliseconds but some scenarios ask for higher time precision, like
in cloud envirenment, we want all the VMs running in the host aquire the
same level accuracy from host clock.

Use of kvm ptp clock, which choose the host clock source clock as a
reference clock to sync time clock between guest and host has been adopted
by x86 which makes the time sync order from milliseconds to nanoseconds.

This patch enable kvm ptp on arm64 and we get the similar clock drift as
found with x86 with kvm ptp.

Test result comparison between with kvm ptp and without it in arm64 are
as follows. This test derived from the result of command 'chronyc
sources'. we should take more cure of the last sample column which shows
the offset between the local clock and the source at the last measurement.

no kvm ptp in guest:
MS Name/IP address Stratum Poll Reach LastRx Last sample
========================================================================
^* dns1.synet.edu.cn 2 6 377 13 +1040us[+1581us] +/- 21ms
^* dns1.synet.edu.cn 2 6 377 21 +1040us[+1581us] +/- 21ms
^* dns1.synet.edu.cn 2 6 377 29 +1040us[+1581us] +/- 21ms
^* dns1.synet.edu.cn 2 6 377 37 +1040us[+1581us] +/- 21ms
^* dns1.synet.edu.cn 2 6 377 45 +1040us[+1581us] +/- 21ms
^* dns1.synet.edu.cn 2 6 377 53 +1040us[+1581us] +/- 21ms
^* dns1.synet.edu.cn 2 6 377 61 +1040us[+1581us] +/- 21ms
^* dns1.synet.edu.cn 2 6 377 4 -130us[ +796us] +/- 21ms
^* dns1.synet.edu.cn 2 6 377 12 -130us[ +796us] +/- 21ms
^* dns1.synet.edu.cn 2 6 377 20 -130us[ +796us] +/- 21ms

in host:
MS Name/IP address Stratum Poll Reach LastRx Last sample
========================================================================
^* 120.25.115.20 2 7 377 72 -470us[ -603us] +/- 18ms
^* 120.25.115.20 2 7 377 92 -470us[ -603us] +/- 18ms
^* 120.25.115.20 2 7 377 112 -470us[ -603us] +/- 18ms
^* 120.25.115.20 2 7 377 2 +872ns[-6808ns] +/- 17ms
^* 120.25.115.20 2 7 377 22 +872ns[-6808ns] +/- 17ms
^* 120.25.115.20 2 7 377 43 +872ns[-6808ns] +/- 17ms
^* 120.25.115.20 2 7 377 63 +872ns[-6808ns] +/- 17ms
^* 120.25.115.20 2 7 377 83 +872ns[-6808ns] +/- 17ms
^* 120.25.115.20 2 7 377 103 +872ns[-6808ns] +/- 17ms
^* 120.25.115.20 2 7 377 123 +872ns[-6808ns] +/- 17ms

The dns1.synet.edu.cn is the network reference clock for guest and
120.25.115.20 is the network reference clock for host. we can't get the
clock error between guest and host directly, but a roughly estimated value
will be in order of hundreds of us to ms.

with kvm ptp in guest:
chrony has been disabled in host to remove the disturb by network clock.

MS Name/IP address Stratum Poll Reach LastRx Last sample
========================================================================
* PHC0 0 3 377 8 -7ns[ +1ns] +/- 3ns
* PHC0 0 3 377 8 +1ns[ +16ns] +/- 3ns
* PHC0 0 3 377 6 -4ns[ -0ns] +/- 6ns
* PHC0 0 3 377 6 -8ns[ -12ns] +/- 5ns
* PHC0 0 3 377 5 +2ns[ +4ns] +/- 4ns
* PHC0 0 3 377 13 +2ns[ +4ns] +/- 4ns
* PHC0 0 3 377 12 -4ns[ -6ns] +/- 4ns
* PHC0 0 3 377 11 -8ns[ -11ns] +/- 6ns
* PHC0 0 3 377 10 -14ns[ -20ns] +/- 4ns
* PHC0 0 3 377 8 +4ns[ +5ns] +/- 4ns

The PHC0 is the ptp clock which choose the host clock as its source
clock. So we can be sure to say that the clock error between host and guest
is in order of ns.

Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
---
drivers/clocksource/arm_arch_timer.c | 22 ++++++++++++
drivers/ptp/Kconfig | 2 +-
drivers/ptp/ptp_kvm_arm64.c | 53 ++++++++++++++++++++++++++++
3 files changed, 76 insertions(+), 1 deletion(-)
create mode 100644 drivers/ptp/ptp_kvm_arm64.c

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 277846decd33..72260b66f02e 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -1636,3 +1636,25 @@ static int __init arch_timer_acpi_init(struct acpi_table_header *table)
}
TIMER_ACPI_DECLARE(arch_timer, ACPI_SIG_GTDT, arch_timer_acpi_init);
#endif
+
+#if IS_ENABLED(CONFIG_PTP_1588_CLOCK_KVM)
+#include <linux/arm-smccc.h>
+int kvm_arch_ptp_get_crosststamp(unsigned long *cycle, struct timespec64 *ts,
+ struct clocksource **cs)
+{
+ struct arm_smccc_res hvc_res;
+ ktime_t ktime_overall;
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID, &hvc_res);
+ if ((long)(hvc_res.a0) < 0)
+ return -EOPNOTSUPP;
+
+ ktime_overall = hvc_res.a0 << 32 | hvc_res.a1;
+ *ts = ktime_to_timespec64(ktime_overall);
+ *cycle = hvc_res.a2 << 32 | hvc_res.a3;
+ *cs = &clocksource_counter;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_arch_ptp_get_crosststamp);
+#endif
diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig
index 9b8fee5178e8..3c31ff8eb05f 100644
--- a/drivers/ptp/Kconfig
+++ b/drivers/ptp/Kconfig
@@ -110,7 +110,7 @@ config PTP_1588_CLOCK_PCH
config PTP_1588_CLOCK_KVM
tristate "KVM virtual PTP clock"
depends on PTP_1588_CLOCK
- depends on KVM_GUEST && X86
+ depends on KVM_GUEST && X86 || ARM64 && ARM_ARCH_TIMER
default y
help
This driver adds support for using kvm infrastructure as a PTP
diff --git a/drivers/ptp/ptp_kvm_arm64.c b/drivers/ptp/ptp_kvm_arm64.c
new file mode 100644
index 000000000000..f3f957117865
--- /dev/null
+++ b/drivers/ptp/ptp_kvm_arm64.c
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Virtual PTP 1588 clock for use with KVM guests
+ * Copyright (C) 2019 ARM Ltd.
+ * All Rights Reserved
+ */
+
+#include <linux/kernel.h>
+#include <linux/err.h>
+#include <asm/hypervisor.h>
+#include <linux/module.h>
+#include <linux/psci.h>
+#include <linux/arm-smccc.h>
+#include <linux/timecounter.h>
+#include <linux/sched/clock.h>
+#include <asm/arch_timer.h>
+
+int kvm_arch_ptp_init(void)
+{
+ struct arm_smccc_res hvc_res;
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID,
+ &hvc_res);
+ if ((long)(hvc_res.a0) < 0)
+ return -EOPNOTSUPP;
+
+ return 0;
+}
+
+int kvm_arch_ptp_get_clock_generic(struct timespec64 *ts,
+ struct arm_smccc_res *hvc_res)
+{
+ ktime_t ktime_overall;
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID,
+ hvc_res);
+ if ((long)(hvc_res->a0) < 0)
+ return -EOPNOTSUPP;
+
+ ktime_overall = hvc_res->a0 << 32 | hvc_res->a1;
+ *ts = ktime_to_timespec64(ktime_overall);
+
+ return 0;
+}
+
+int kvm_arch_ptp_get_clock(struct timespec64 *ts)
+{
+ struct arm_smccc_res hvc_res;
+
+ kvm_arch_ptp_get_clock_generic(ts, &hvc_res);
+
+ return 0;
+}
--
2.17.1