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SubjectRE: [RFC PATCH 3/3] Enable ptp_kvm for arm64
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Hi Marc,

Very sorry to have missed this comments.

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Thursday, August 29, 2019 6:33 PM
> To: Jianyong Wu (Arm Technology China) <Jianyong.Wu@arm.com>;
> netdev@vger.kernel.org; pbonzini@redhat.com;
> sean.j.christopherson@intel.com; richardcochran@gmail.com; Mark Rutland
> <Mark.Rutland@arm.com>; Will Deacon <Will.Deacon@arm.com>; Suzuki
> Poulose <Suzuki.Poulose@arm.com>
> Cc: linux-kernel@vger.kernel.org; Steve Capper <Steve.Capper@arm.com>;
> Kaly Xin (Arm Technology China) <Kaly.Xin@arm.com>; Justin He (Arm
> Technology China) <Justin.He@arm.com>
> Subject: Re: [RFC PATCH 3/3] Enable ptp_kvm for arm64
>
> 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?
>

Not really, NTP will change the the host clock which will contaminate the data of sync between
Host and guest. But in reality, we will keep NTP online.

> >
> > 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.
>
Ok, really better.

> >
> > 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).
>
The code here is really ugly, I need a better solution to offer a clock source
For the guest.

> 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.
>
I think it really necessary.

> 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.
>
I can have a try, but the detail is not clear for me now.

> > +
> > #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.
>
Err, sorry, what's mean of "link the two parts there"? should I add another two file update driver/ptp/
Both for arm64 and x86 to contains these arch-specific code or pack them all into ptp_kvm.c?

> > 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...

Yeah, ns is really redundant.

>
> > +}
> > +
> > +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_FU
> NC_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_FU
> NC_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()?
>

Yeah, it's better.

> > +
> > +MODULE_AUTHOR("Marcelo Tosatti <mtosatti@redhat.com>");
> > +MODULE_DESCRIPTION("PTP clock using KVMCLOCK");
> > +MODULE_LICENSE("GPL");
>
> This should only exist in the generic code.

Ok. I will remove them.

>
> > 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.
>
Ok.

> >
> > 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

Yeah

>
> > + */
> > + 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.

One api of ptp_kvm called ptp_kvm_get_time_fn need a clock sources passed from host as system_counter.
>
> > + val[3] = 0;
> > + break;
>
> This will probably conflict with Steven's stolen time series. Not a big deal
> though.
Err, sorry I am not familiar with this theory. Let me check it.

>
> > 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?
>
I think it won't solve the problem generated by VM migration and only for VMs in a single machine.
Ptp_kvm only works for VMs in the same machine.
But using ptp (not ptp_kvm) clock, all the machines in a low latency network environment can keep time sync in high precision,
Then VMs move from one machine to another will obtain a high precision time sync.

Thanks
Jianyong Wu

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