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SubjectRe: [RFC PATCH 3/3] Enable ptp_kvm for arm64
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On 29/08/2019 07:39, Jianyong Wu wrote:
> 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.

Is that a realistic use case? Why should the host not use NTP?

>
> 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>
> ---
> arch/arm64/include/asm/arch_timer.h | 3 ++
> arch/arm64/kvm/arch_ptp_kvm.c | 76 ++++++++++++++++++++++++++++
> drivers/clocksource/arm_arch_timer.c | 6 ++-
> drivers/ptp/Kconfig | 2 +-
> include/linux/arm-smccc.h | 14 +++++
> virt/kvm/arm/psci.c | 17 +++++++
> 6 files changed, 115 insertions(+), 3 deletions(-)
> create mode 100644 arch/arm64/kvm/arch_ptp_kvm.c

Please split this patch into two parts: the hypervisor code in a patch
and the guest code in another patch. Having both of them together is
confusing.

>
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index 6756178c27db..880576a814b6 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -229,4 +229,7 @@ static inline int arch_timer_arch_init(void)
> return 0;
> }
>
> +extern struct clocksource clocksource_counter;
> +extern u64 arch_counter_read(struct clocksource *cs);

I'm definitely not keen on exposing the internals of the arch_timer
driver to random subsystems. Furthermore, you seem to expect that the
guest kernel will only use the arch timer as a clocksource, and nothing
really guarantees that (in which case get_device_system_crosststamp will
fail).

It looks to me that we'd be better off exposing a core timekeeping API
that populates a struct system_counterval_t based on the *current*
timekeeper monotonic clocksource. This would simplify the split between
generic and arch-specific code.

Whether or not tglx will be happy with the idea is another problem, but
I'm certainly not taking any change to the arch timer code based on this.

> +
> #endif
> diff --git a/arch/arm64/kvm/arch_ptp_kvm.c b/arch/arm64/kvm/arch_ptp_kvm.c

We don't put non-hypervisor in arch/arm64/kvm. Please move it back to
drivers/ptp (as well as its x86 counterpart), and just link the two
parts there. This should also allow this to be enabled for 32bit guests.

> new file mode 100644
> index 000000000000..6b2165ebce62
> --- /dev/null
> +++ b/arch/arm64/kvm/arch_ptp_kvm.c
> @@ -0,0 +1,76 @@
> +// 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 <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>
> +
> +/*
> + * as trap call cause delay, this function will return the delay in nanosecond
> + */
> +static u64 arm_smccc_1_1_invoke_delay(u32 id, struct arm_smccc_res *res)
> +{
> + u64 ns, t1, t2;
> +
> + t1 = sched_clock();
> + arm_smccc_1_1_invoke(id, res);
> + t2 = sched_clock();
> + t2 -= t1;
> + ns = t2;
> + return ns;

I think you can get rid of the ns variable here...

> +}
> +
> +int kvm_arch_ptp_init(void)
> +{
> + return 0;
> +}
> +
> +int kvm_arch_ptp_get_clock(struct timespec64 *ts)
> +{
> + u64 ns;
> + struct arm_smccc_res hvc_res;
> +
> + if (!kvm_arm_hyp_service_available(
> + ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID)) {
> + return -EOPNOTSUPP;
> + }
> + ns = arm_smccc_1_1_invoke_delay(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID,
> + &hvc_res);
> + ts->tv_sec = hvc_res.a0;
> + ts->tv_nsec = hvc_res.a1;
> + timespec64_add_ns(ts, ns);
> + return 0;
> +}
> +
> +int kvm_arch_ptp_get_clock_fn(long *cycle, struct timespec64 *ts,
> + struct clocksource **cs)
> +{
> + u64 ns;
> + struct arm_smccc_res hvc_res;
> +
> + if (!kvm_arm_hyp_service_available(
> + ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID)) {
> + return -EOPNOTSUPP;
> + }
> + ns = arm_smccc_1_1_invoke_delay(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID,
> + &hvc_res);
> + ts->tv_sec = hvc_res.a0;
> + ts->tv_nsec = hvc_res.a1;
> + timespec64_add_ns(ts, ns);
> + *cycle = hvc_res.a2;
> + *cs = &clocksource_counter;
> +
> + return 0;
> +}

Why do we have two functions doing almost the same thing? Why do you
call kvm_arm_hyp_service_available on each and every time? Isn't it
enough to check in kvm_arch_ptp_init()?

> +
> +MODULE_AUTHOR("Marcelo Tosatti <mtosatti@redhat.com>");
> +MODULE_DESCRIPTION("PTP clock using KVMCLOCK");
> +MODULE_LICENSE("GPL");

This should only exist in the generic code.

> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 07e57a49d1e8..021e3f69364c 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -175,23 +175,25 @@ static notrace u64 arch_counter_get_cntvct(void)
> u64 (*arch_timer_read_counter)(void) = arch_counter_get_cntvct;
> EXPORT_SYMBOL_GPL(arch_timer_read_counter);
>
> -static u64 arch_counter_read(struct clocksource *cs)
> +u64 arch_counter_read(struct clocksource *cs)
> {
> return arch_timer_read_counter();
> }
> +EXPORT_SYMBOL(arch_counter_read);
>
> static u64 arch_counter_read_cc(const struct cyclecounter *cc)
> {
> return arch_timer_read_counter();
> }
>
> -static struct clocksource clocksource_counter = {
> +struct clocksource clocksource_counter = {
> .name = "arch_sys_counter",
> .rating = 400,
> .read = arch_counter_read,
> .mask = CLOCKSOURCE_MASK(56),
> .flags = CLOCK_SOURCE_IS_CONTINUOUS,
> };
> +EXPORT_SYMBOL(clocksource_counter);

I've said what I thought about this. Not happening.

>
> static struct cyclecounter cyclecounter __ro_after_init = {
> .read = arch_counter_read_cc,
> diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig
> index 9b8fee5178e8..e032fafdafa7 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
> default y
> help
> This driver adds support for using kvm infrastructure as a PTP
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index a6e4d3e3d10a..2a222a1a8594 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -94,6 +94,7 @@
>
> /* KVM "vendor specific" services */
> #define ARM_SMCCC_KVM_FUNC_FEATURES 0
> +#define ARM_SMCCC_KVM_PTP 1
> #define ARM_SMCCC_KVM_FUNC_FEATURES_2 127
> #define ARM_SMCCC_KVM_NUM_FUNCS 128
>
> @@ -102,6 +103,16 @@
> ARM_SMCCC_SMC_32, \
> ARM_SMCCC_OWNER_VENDOR_HYP, \
> ARM_SMCCC_KVM_FUNC_FEATURES)
> +/*
> + * This ID used for virtual ptp kvm clock and it will pass second value
> + * and nanosecond value of host real time and system counter by vcpu
> + * register to guest.
> + */
> +#define ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID \
> + ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \
> + ARM_SMCCC_SMC_32, \
> + ARM_SMCCC_OWNER_VENDOR_HYP, \
> + ARM_SMCCC_KVM_PTP)
>
> #ifndef __ASSEMBLY__
>
> @@ -373,5 +384,8 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,
> method; \
> })
>
> +#include <linux/psci.h>
> +#include <linux/clocksource.h>
> +
> #endif /*__ASSEMBLY__*/
> #endif /*__LINUX_ARM_SMCCC_H*/
> diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c
> index 0debf49bf259..7fffdb25d32c 100644
> --- a/virt/kvm/arm/psci.c
> +++ b/virt/kvm/arm/psci.c
> @@ -392,6 +392,8 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> u32 func_id = smccc_get_function(vcpu);
> u32 val[4] = {};
> u32 option;
> + struct timespec *ts;
> + u64 cnt;
>
> val[0] = SMCCC_RET_NOT_SUPPORTED;
>
> @@ -431,6 +433,21 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
> val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
> break;
> + /*
> + * This will used for virtual ptp kvm clock. three
> + * values will be passed back.
> + * reg0 stores seconds of host real time;
> + * reg1 stores nanoseconds of host real time;
> + * reg2 stotes system counter cycle value.

stores

> + */
> + case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
> + getnstimeofday(ts);
> + cnt = arch_timer_read_counter();
> + val[0] = ts->tv_sec;
> + val[1] = ts->tv_nsec;
> + val[2] = cnt;

Can you explain what the purpose of exposing this counter is? The guest
should have access to the physical counter already.

> + val[3] = 0;
> + break;

This will probably conflict with Steven's stolen time series. Not a big
deal though.

> default:
> return kvm_psci_call(vcpu);
> }
>

Other questions: how does this works with VM migration? Specially when
moving from a hypervisor that supports the feature to one that doesn't?

Thanks,

M.
--
Jazz is not dead, it just smells funny...

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