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From:   Jianyong Wu <Jianyong.Wu@arm.com>
To:     Marc Zyngier <maz@kernel.org>,
        "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>,
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        Mark Rutland <Mark.Rutland@arm.com>,
        "will@kernel.org" <will@kernel.org>,
        Suzuki Poulose <Suzuki.Poulose@arm.com>,
        Andre Przywara <Andre.Przywara@arm.com>,
        Steven Price <Steven.Price@arm.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Sudeep Holla <Sudeep.Holla@arm.com>
CC:     "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>,
        "kernel-team@android.com" <kernel-team@android.com>,
        Mark Rutland <Mark.Rutland@arm.com>
Subject: RE: [PATCH v18 7/7] ptp: arm/arm64: Enable ptp_kvm for arm/arm64
Thread-Topic: [PATCH v18 7/7] ptp: arm/arm64: Enable ptp_kvm for arm/arm64
Thread-Index: AQHW/iAeZDUirA6w+ESkcbI2x50VbqqcmonQ
Date:   Tue, 30 Mar 2021 10:05:22 +0000
Message-ID: <AM5PR0801MB20820473E5882F4AD344C96AF47D9@AM5PR0801MB2082.eurprd08.prod.outlook.com>
References: <20210208134029.3269384-1-maz@kernel.org>
 <20210208134029.3269384-8-maz@kernel.org>
In-Reply-To: <20210208134029.3269384-8-maz@kernel.org>
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-----Original Message-----
From: Marc Zyngier <maz@kernel.org>=20
Sent: Monday, February 8, 2021 9:40 PM
To: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org; tglx=
@linutronix.de; pbonzini@redhat.com; seanjc@google.com; richardcochran@gmai=
l.com; Mark Rutland <Mark.Rutland@arm.com>; will@kernel.org; Suzuki Poulose=
 <Suzuki.Poulose@arm.com>; Andre Przywara <Andre.Przywara@arm.com>; Steven =
Price <Steven.Price@arm.com>; Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>=
; Sudeep Holla <Sudeep.Holla@arm.com>
Cc: linux-kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; kvm=
arm@lists.cs.columbia.edu; kvm@vger.kernel.org; Steve Capper <Steve.Capper@=
arm.com>; Justin He <Justin.He@arm.com>; Jianyong Wu <Jianyong.Wu@arm.com>;=
 kernel-team@android.com; Mark Rutland <Mark.Rutland@arm.com>
Subject: [PATCH v18 7/7] ptp: arm/arm64: Enable ptp_kvm for arm/arm64

From: Jianyong Wu <jianyong.wu@arm.com>

Currently, there is no mechanism to keep time sync between guest and host i=
n arm/arm64 virtualization environment. Time in guest will drift compared w=
ith host after boot up as they may both use third party time sources to cor=
rect their time respectively. The time deviation will be in order of millis=
econds. But in some scenarios,like in cloud environment, we ask for higher =
time precision.

kvm ptp clock, which chooses the host clock source as a reference clock to =
sync time between guest and host, has been adopted by x86 which takes the t=
ime sync order from milliseconds to nanoseconds.

This patch enables kvm ptp clock for arm/arm64 and improves clock sync prec=
ision significantly.

Test result comparisons between with kvm ptp clock and without it in arm/ar=
m64 are as follows. This test derived from the result of command 'chronyc s=
ources'. 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
=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] +/-   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
=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] +/-   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 clo=
ck error between guest and host directly, but a roughly estimated value wil=
l 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] +/-    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.

Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201209060932.212364-8-jianyong.wu@arm.com
---
 drivers/clocksource/arm_arch_timer.c | 34 ++++++++++++++++++++++++++++
 drivers/ptp/Kconfig                  |  2 +-
 drivers/ptp/Makefile                 |  1 +
 drivers/ptp/ptp_kvm_arm.c            | 28 +++++++++++++++++++++++
 4 files changed, 64 insertions(+), 1 deletion(-)  create mode 100644 drive=
rs/ptp/ptp_kvm_arm.c

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm=
_arch_timer.c
index 8f12e223703f..e0f167e5e792 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -25,6 +25,8 @@
 #include <linux/sched/clock.h>
 #include <linux/sched_clock.h>
 #include <linux/acpi.h>
+#include <linux/arm-smccc.h>
+#include <linux/ptp_kvm.h>
=20
 #include <asm/arch_timer.h>
 #include <asm/virt.h>
@@ -1659,3 +1661,35 @@ static int __init arch_timer_acpi_init(struct acpi_t=
able_header *table)  }  TIMER_ACPI_DECLARE(arch_timer, ACPI_SIG_GTDT, arch_=
timer_acpi_init);  #endif
+
+int kvm_arch_ptp_get_crosststamp(u64 *cycle, struct timespec64 *ts,
+				 struct clocksource **cs)
+{
+	struct arm_smccc_res hvc_res;
+	u32 ptp_counter;
+	ktime_t ktime;
+
+	if (!IS_ENABLED(CONFIG_HAVE_ARM_SMCCC_DISCOVERY))
+		return -EOPNOTSUPP;
+
+	if (arch_timer_uses_ppi =3D=3D ARCH_TIMER_VIRT_PPI)
+		ptp_counter =3D KVM_PTP_VIRT_COUNTER;
+	else
+		ptp_counter =3D KVM_PTP_PHYS_COUNTER;
+
+	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID,
+			     ptp_counter, &hvc_res);
+
+	if ((int)(hvc_res.a0) < 0)
+		return -EOPNOTSUPP;
+
+	ktime =3D (u64)hvc_res.a0 << 32 | hvc_res.a1;
+	*ts =3D ktime_to_timespec64(ktime);
+	if (cycle)
+		*cycle =3D (u64)hvc_res.a2 << 32 | hvc_res.a3;
+	if (cs)
+		*cs =3D &clocksource_counter;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_arch_ptp_get_crosststamp);
diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig index f2edef0df40f..=
8c20e524e9ad 100644
--- a/drivers/ptp/Kconfig
+++ b/drivers/ptp/Kconfig
@@ -108,7 +108,7 @@ 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) || (HAVE_ARM_SMCCC_DISCOVERY &&=20
+ARM_ARCH_TIMER)
 	default y
 	help
 	  This driver adds support for using kvm infrastructure as a PTP diff --g=
it a/drivers/ptp/Makefile b/drivers/ptp/Makefile index d11eeb5811d1..8673d1=
743faa 100644
--- a/drivers/ptp/Makefile
+++ b/drivers/ptp/Makefile
@@ -5,6 +5,7 @@
=20
 ptp-y					:=3D ptp_clock.o ptp_chardev.o ptp_sysfs.o
 ptp_kvm-$(CONFIG_X86)			:=3D ptp_kvm_x86.o ptp_kvm_common.o
+ptp_kvm-$(CONFIG_HAVE_ARM_SMCCC)	:=3D ptp_kvm_arm.o ptp_kvm_common.o
 obj-$(CONFIG_PTP_1588_CLOCK)		+=3D ptp.o
 obj-$(CONFIG_PTP_1588_CLOCK_DTE)	+=3D ptp_dte.o
 obj-$(CONFIG_PTP_1588_CLOCK_INES)	+=3D ptp_ines.o
diff --git a/drivers/ptp/ptp_kvm_arm.c b/drivers/ptp/ptp_kvm_arm.c new file=
 mode 100644 index 000000000000..b7d28c8dfb84
--- /dev/null
+++ b/drivers/ptp/ptp_kvm_arm.c
@@ -0,0 +1,28 @@
+// 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/arm-smccc.h>
+#include <linux/ptp_kvm.h>
+
+#include <asm/arch_timer.h>
+#include <asm/hypervisor.h>
+
+int kvm_arch_ptp_init(void)
+{
+	int ret;
+
+	ret =3D kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_PTP);
+	if (ret <=3D 0)
+		return -EOPNOTSUPP;
+
+	return 0;
+}
+
+int kvm_arch_ptp_get_clock(struct timespec64 *ts) {
+	return kvm_arch_ptp_get_crosststamp(NULL, ts, NULL); }
--
2.29.2