[RFC PATCH 3/3] Enable ptp_kvm for arm64

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

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.

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

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);
+
 #endif
diff --git a/arch/arm64/kvm/arch_ptp_kvm.c b/arch/arm64/kvm/arch_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;
+}
+
+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_FUNC_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_FUNC_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;
+}
+
+MODULE_AUTHOR("Marcelo Tosatti <mtosatti@redhat.com>");
+MODULE_DESCRIPTION("PTP clock using KVMCLOCK");
+MODULE_LICENSE("GPL");
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);
 
 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.
+	 */
+	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;
+		val[3] = 0;
+		break;
 	default:
 		return kvm_psci_call(vcpu);
 	}
-- 
2.17.1