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From:   Jianyong Wu <Jianyong.Wu@arm.com>
To:     Marc Zyngier <maz@kernel.org>
CC:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "yangbo.lu@nxp.com" <yangbo.lu@nxp.com>,
        "john.stultz@linaro.org" <john.stultz@linaro.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "sean.j.christopherson@intel.com" <sean.j.christopherson@intel.com>,
        "richardcochran@gmail.com" <richardcochran@gmail.com>,
        Mark Rutland <Mark.Rutland@arm.com>,
        "will@kernel.org" <will@kernel.org>,
        Suzuki Poulose <Suzuki.Poulose@arm.com>,
        Steven Price <Steven.Price@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Steve Capper <Steve.Capper@arm.com>,
        Justin He <Justin.He@arm.com>, nd <nd@arm.com>
Subject: RE: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
Thread-Topic: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
Thread-Index: AQHWgp4Q48WtGxJp4kuFSJTL6o01LqlZ4qMAgAL3/tA=
Date:   Mon, 7 Sep 2020 08:40:34 +0000
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        <20200904092744.167655-9-jianyong.wu@arm.com> <874kocmqqx.wl-maz@kernel.org>
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Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Saturday, September 5, 2020 7:02 PM
> To: Jianyong Wu <Jianyong.Wu@arm.com>
> Cc: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org;
> tglx@linutronix.de; pbonzini@redhat.com; sean.j.christopherson@intel.com;
> richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>;
> will@kernel.org; Suzuki Poulose <Suzuki.Poulose@arm.com>; Steven Price
> <Steven.Price@arm.com>; linux-kernel@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
> kvm@vger.kernel.org; Steve Capper <Steve.Capper@arm.com>; Justin He
> <Justin.He@arm.com>; nd <nd@arm.com>
> Subject: Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64
>=20
> On Fri, 04 Sep 2020 10:27:42 +0100,
> Jianyong Wu <jianyong.wu@arm.com> 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 la=
st
> measurement.
> >
> > no kvm ptp in guest:
> > MS Name/IP address   Stratum Poll Reach LastRx Last sample
> >
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > ^* dns1.synet.edu.cn      2   6   377    13  +1040us[+1581us] +/-   21m=
s
> > ^* dns1.synet.edu.cn      2   6   377    21  +1040us[+1581us] +/-   21m=
s
> > ^* dns1.synet.edu.cn      2   6   377    29  +1040us[+1581us] +/-   21m=
s
> > ^* dns1.synet.edu.cn      2   6   377    37  +1040us[+1581us] +/-   21m=
s
> > ^* dns1.synet.edu.cn      2   6   377    45  +1040us[+1581us] +/-   21m=
s
> > ^* dns1.synet.edu.cn      2   6   377    53  +1040us[+1581us] +/-   21m=
s
> > ^* dns1.synet.edu.cn      2   6   377    61  +1040us[+1581us] +/-   21m=
s
> > ^* dns1.synet.edu.cn      2   6   377     4   -130us[ +796us] +/-   21m=
s
> > ^* dns1.synet.edu.cn      2   6   377    12   -130us[ +796us] +/-   21m=
s
> > ^* dns1.synet.edu.cn      2   6   377    20   -130us[ +796us] +/-   21m=
s
> >
> > in host:
> > MS Name/IP address   Stratum Poll Reach LastRx Last sample
> >
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > ^* 120.25.115.20          2   7   377    72   -470us[ -603us] +/-   18m=
s
> > ^* 120.25.115.20          2   7   377    92   -470us[ -603us] +/-   18m=
s
> > ^* 120.25.115.20          2   7   377   112   -470us[ -603us] +/-   18m=
s
> > ^* 120.25.115.20          2   7   377     2   +872ns[-6808ns] +/-   17m=
s
> > ^* 120.25.115.20          2   7   377    22   +872ns[-6808ns] +/-   17m=
s
> > ^* 120.25.115.20          2   7   377    43   +872ns[-6808ns] +/-   17m=
s
> > ^* 120.25.115.20          2   7   377    63   +872ns[-6808ns] +/-   17m=
s
> > ^* 120.25.115.20          2   7   377    83   +872ns[-6808ns] +/-   17m=
s
> > ^* 120.25.115.20          2   7   377   103   +872ns[-6808ns] +/-   17m=
s
> > ^* 120.25.115.20          2   7   377   123   +872ns[-6808ns] +/-   17m=
s
> >
> > 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
> >
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > * PHC0                    0   3   377     8     -7ns[   +1ns] +/-    3n=
s
> > * PHC0                    0   3   377     8     +1ns[  +16ns] +/-    3n=
s
> > * PHC0                    0   3   377     6     -4ns[   -0ns] +/-    6n=
s
> > * PHC0                    0   3   377     6     -8ns[  -12ns] +/-    5n=
s
> > * PHC0                    0   3   377     5     +2ns[   +4ns] +/-    4n=
s
> > * PHC0                    0   3   377    13     +2ns[   +4ns] +/-    4n=
s
> > * PHC0                    0   3   377    12     -4ns[   -6ns] +/-    4n=
s
> > * PHC0                    0   3   377    11     -8ns[  -11ns] +/-    6n=
s
> > * PHC0                    0   3   377    10    -14ns[  -20ns] +/-    4n=
s
> > * PHC0                    0   3   377     8     +4ns[   +5ns] +/-    4n=
s
> >
> > 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 | 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 =3D (long long)hvc_res.a0;
> > +	*ts =3D ktime_to_timespec64(ktime);
> > +	*cycle =3D (long long)hvc_res.a1;
> > +	*cs =3D &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;
>=20
> 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 accep=
table
> behaviour.
>=20
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)
>=20
> 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;
>=20
> 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.
>=20
> > +
> > +	ktime =3D (long long)hvc_res->a0;
> > +	*ts =3D 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
> >
> >
>=20
> 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 attent=
ion
> to this kind of detail.

Yeah,  I will.

Thanks
Jianyong=20
>=20
> 	M.
>=20
> --
> Without deviation from the norm, progress is not possible.