Re: [PATCH v15 7/9] ptp: arm/arm64: Enable ptp_kvm for arm/arm64

Marc Zyngier
2020-11-23T10:49:49Z

On 2020-11-11 06:22, Jianyong Wu wrote:
> 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 envirenment, we
> ask

environment

> 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
> precison

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.
>
> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> ---
> drivers/clocksource/arm_arch_timer.c | 28 ++++++++++++++++++
> drivers/ptp/Kconfig | 2 +-
> drivers/ptp/Makefile | 1 +
> drivers/ptp/ptp_kvm_arm.c | 44 ++++++++++++++++++++++++++++
> 4 files changed, 74 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 d55acffb0b90..b33c5a663d30 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -25,6 +25,7 @@
> #include <linux/sched/clock.h>
> #include <linux/sched_clock.h>
> #include <linux/acpi.h>
> +#include <linux/arm-smccc.h>
>
> #include <asm/arch_timer.h>
> #include <asm/virt.h>
> @@ -1650,3 +1651,30 @@ 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;
> + ktime_t ktime;
> + u32 ptp_counter;
> +
> + if (arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
> + ptp_counter = ARM_PTP_VIRT_COUNTER;
> + else
> + ptp_counter = ARM_PTP_PHY_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);
> + *cycle = (u64)hvc_res.a2 << 32 | hvc_res.a3;

Endianness.

> + *cs = &clocksource_counter;
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_arch_ptp_get_crosststamp);
> diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig
> index 942f72d8151d..677c7f696b70 100644
> --- a/drivers/ptp/Kconfig
> +++ b/drivers/ptp/Kconfig
> @@ -106,7 +106,7 @@ 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 699a4e4d19c2..9fa5ede44b2b 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..2212827c0384
> --- /dev/null
> +++ b/drivers/ptp/ptp_kvm_arm.c
> @@ -0,0 +1,44 @@
> +// 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>
> +#include <asm/hypervisor.h>
> +
> +int kvm_arch_ptp_init(void)
> +{
> + int ret;
> +
> + ret = kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_KVM_PTP);
> + if (ret <= 0)
> + return -EOPNOTSUPP;
> +
> + return 0;
> +}
> +
> +int kvm_arch_ptp_get_clock(struct timespec64 *ts)
> +{
> + ktime_t ktime;
> + struct arm_smccc_res hvc_res;
> +
> + arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID,
> + ARM_PTP_NONE_COUNTER, &hvc_res);

I really don't see the need to use a non-architectural counter ID.
Using the virtual counter ID should just be fine, and shouldn't
lead to any issue.

Am I missing something?

> + if ((int)(hvc_res.a0) < 0)
> + return -EOPNOTSUPP;
> +
> + ktime = (u64)hvc_res.a0 << 32 | hvc_res.a1;

Endianness.

> + *ts = ktime_to_timespec64(ktime);
> +
> + return 0;
> +}

Thanks,

M.
--
Jazz is not dead. It just smells funny...