RE: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64

[Jianyong Wu <Jianyong.Wu@arm.com>]

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Monday, September 7, 2020 4:55 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
> 
> On 2020-09-07 09:40, Jianyong Wu wrote:
> > 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
> >>
> >> 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 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 | 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 "|".
> 
> But even then. (-1 & whatever) is always true.

Yeah, what about checking if a0 is non-negative first? Like:
if (hvc_res.a0 < 0 || !(hvc_res.a0 & BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP)))
	return -EOPNOTSUPP;

Thanks
Jianyong 
> 
>          M.
> --
> Jazz is not dead. It just smells funny...