Hi Marc,
> -----Original Message-----
> From: Marc Zyngier <maz@xxxxxxxxxx>
> Sent: Saturday, September 5, 2020 7:02 PM
> To: Jianyong Wu <Jianyong.Wu@xxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; yangbo.lu@xxxxxxx; john.stultz@xxxxxxxxxx;
> tglx@xxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; sean.j.christopherson@xxxxxxxxx;
> richardcochran@xxxxxxxxx; Mark Rutland <Mark.Rutland@xxxxxxx>;
> will@xxxxxxxxxx; Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Steven Price
> <Steven.Price@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx;
> kvm@xxxxxxxxxxxxxxx; Steve Capper <Steve.Capper@xxxxxxx>; Justin He
> <Justin.He@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
>
> On Fri, 04 Sep 2020 10:27:42 +0100,
> Jianyong Wu <jianyong.wu@xxxxxxx> wrote:
> >
> > Currently, there is no mechanism to keep time sync between guest and
> > host in 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 for higher time precision.
> >
> > kvm ptp clock, which choose the host clock source as a reference clock
> > to sync time between guest and host, has been adopted by x86 which
> > makes the time sync order from milliseconds to nanoseconds.
> >
> > This patch enables kvm ptp clock for arm64 and improve clock sync
> > precison significantly.
> >
> > Test result comparisons between with kvm ptp clock and without it in
> > 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@xxxxxxx>
> > ---
> > drivers/clocksource/arm_arch_timer.c | 24 +++++++++++++
> > drivers/ptp/Kconfig | 2 +-
> > drivers/ptp/ptp_kvm_arm64.c | 53
> ++++++++++++++++++++++++++++
> > 3 files changed, 78 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 d55acffb0b90..aaf286e90092 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> > @@ -1650,3 +1650,27 @@ 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;
> > +
> > + /* Currently, linux guest will always use the virtual counter */
> > +
> arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU
> NC_ID,
> > + ARM_PTP_VIRT_COUNTER, &hvc_res);
> > + if ((long long)(hvc_res.a0) < 0)
> > + return -EOPNOTSUPP;
> > +
> > + ktime = (long long)hvc_res.a0;
> > + *ts = ktime_to_timespec64(ktime);
> > + *cycle = (long long)hvc_res.a1;
> > + *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
> > 942f72d8151d..127e96f14f89 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 || ARM64 && ARM_ARCH_TIMER
> &&
> > +ARM_PSCI_FW
> > 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..961abed93dfd
> > --- /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_FEATUR
> ES_FUNC_ID,
> > + &hvc_res);
> > + if (!(hvc_res.a0 | BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP)))
> > + return -EOPNOTSUPP;
> > +
> > + return 0;
>
> What happens if the
> ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID function isn't
> implemented (on an old kernel or a non-KVM hypervisor)? The expected
> behaviour is that a0 will contain SMCCC_RET_NOT_SUPPORTED, which is -1.
> The result is that this function always returns "supported". Not an acceptable
> behaviour.
>
Oh! it's really a stupid mistake, should be "&" not "|".
> > +}
> > +
> > +int kvm_arch_ptp_get_clock_generic(struct timespec64 *ts,
> > + struct arm_smccc_res *hvc_res)
>
> Why isn't this static?
>
yeah, should be static.
> > +{
> > + ktime_t ktime;
> > +
> > +
> arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU
> NC_ID,
> > + hvc_res);
> > + if ((long long)(hvc_res->a0) < 0)
> > + return -EOPNOTSUPP;
>
> Really? What if the cycle counter is a full 64 bit value, as it is
> *mandated* on ARMv8.6? It means that the counter is now invalid for half
> the lifetime of the system. Not acceptable either.
>
> > +
> > + ktime = (long long)hvc_res->a0;
> > + *ts = ktime_to_timespec64(ktime);
> > +
> > + 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
> >
> >
>
> It is now obvious that the API between kernel and hypervisor is pretty
> busted, and it goes beyond the 32bit support. I wish you paid more attention
> to this kind of detail.
Yeah, I will.
Thanks
Jianyong
>
> M.
>
> --
> Without deviation from the norm, progress is not possible.
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