[PATCH v18 7/7] ptp: arm/arm64: Enable ptp_kvm for arm/arm64

Marc Zyngier
2021-02-08T13:45:28Z

From: Jianyong Wu <jianyong.wu@arm.com>

Currently, there is no mechanism to keep time sync between guest and host
in arm/arm64 virtualization environment. 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 in some scenarios,like in cloud environment, we ask
for higher time precision.

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

This patch enables kvm ptp clock for arm/arm64 and improves clock sync precision
significantly.

Test result comparisons between with kvm ptp clock and without it in arm/arm64
are as follows. This test derived from the result of command 'chronyc
sources'. we should take more care 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 see that the clock difference between host and guest
is in order of ns.

Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201209060932.212364-8-jianyong.wu@arm.com
---
drivers/clocksource/arm_arch_timer.c | 34 ++++++++++++++++++++++++++++
drivers/ptp/Kconfig | 2 +-
drivers/ptp/Makefile | 1 +
drivers/ptp/ptp_kvm_arm.c | 28 +++++++++++++++++++++++
4 files changed, 64 insertions(+), 1 deletion(-)
create mode 100644 drivers/ptp/ptp_kvm_arm.c

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 8f12e223703f..e0f167e5e792 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -25,6 +25,8 @@
#include <linux/sched/clock.h>
#include <linux/sched_clock.h>
#include <linux/acpi.h>
+#include <linux/arm-smccc.h>
+#include <linux/ptp_kvm.h>

#include <asm/arch_timer.h>
#include <asm/virt.h>
@@ -1659,3 +1661,35 @@ 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
+
+int kvm_arch_ptp_get_crosststamp(u64 *cycle, struct timespec64 *ts,
+ struct clocksource **cs)
+{
+ struct arm_smccc_res hvc_res;
+ u32 ptp_counter;
+ ktime_t ktime;
+
+ if (!IS_ENABLED(CONFIG_HAVE_ARM_SMCCC_DISCOVERY))
+ return -EOPNOTSUPP;
+
+ if (arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
+ ptp_counter = KVM_PTP_VIRT_COUNTER;
+ else
+ ptp_counter = KVM_PTP_PHYS_COUNTER;
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID,
+ ptp_counter, &hvc_res);
+
+ if ((int)(hvc_res.a0) < 0)
+ return -EOPNOTSUPP;
+
+ ktime = (u64)hvc_res.a0 << 32 | hvc_res.a1;
+ *ts = ktime_to_timespec64(ktime);
+ if (cycle)
+ *cycle = (u64)hvc_res.a2 << 32 | hvc_res.a3;
+ if (cs)
+ *cs = &clocksource_counter;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_arch_ptp_get_crosststamp);
diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig
index f2edef0df40f..8c20e524e9ad 100644
--- a/drivers/ptp/Kconfig
+++ b/drivers/ptp/Kconfig
@@ -108,7 +108,7 @@ 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) || (HAVE_ARM_SMCCC_DISCOVERY && ARM_ARCH_TIMER)
default y
help
This driver adds support for using kvm infrastructure as a PTP
diff --git a/drivers/ptp/Makefile b/drivers/ptp/Makefile
index d11eeb5811d1..8673d1743faa 100644
--- a/drivers/ptp/Makefile
+++ b/drivers/ptp/Makefile
@@ -5,6 +5,7 @@

ptp-y := ptp_clock.o ptp_chardev.o ptp_sysfs.o
ptp_kvm-$(CONFIG_X86) := ptp_kvm_x86.o ptp_kvm_common.o
+ptp_kvm-$(CONFIG_HAVE_ARM_SMCCC) := ptp_kvm_arm.o ptp_kvm_common.o
obj-$(CONFIG_PTP_1588_CLOCK) += ptp.o
obj-$(CONFIG_PTP_1588_CLOCK_DTE) += ptp_dte.o
obj-$(CONFIG_PTP_1588_CLOCK_INES) += ptp_ines.o
diff --git a/drivers/ptp/ptp_kvm_arm.c b/drivers/ptp/ptp_kvm_arm.c
new file mode 100644
index 000000000000..b7d28c8dfb84
--- /dev/null
+++ b/drivers/ptp/ptp_kvm_arm.c
@@ -0,0 +1,28 @@
+// 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/arm-smccc.h>
+#include <linux/ptp_kvm.h>
+
+#include <asm/arch_timer.h>
+#include <asm/hypervisor.h>
+
+int kvm_arch_ptp_init(void)
+{
+ int ret;
+
+ ret = kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_PTP);
+ if (ret <= 0)
+ return -EOPNOTSUPP;
+
+ return 0;
+}
+
+int kvm_arch_ptp_get_clock(struct timespec64 *ts)
+{
+ return kvm_arch_ptp_get_crosststamp(NULL, ts, NULL);
+}
--
2.29.2