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KVM virtual PTP driver (v2)

PATCH New Marcelo Tosatti 1 participant 4 messages Jan 13, 2017

Subsystems (7)
Network drivers Documentation x86 KVM +3 more subsystems
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Marcelo Tosatti

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#0 lore raw

cover KVM virtual PTP driver (v2)

This patchset implements a virtual PTP driver which allows guest to sync its clock to the host clock with high precision ( error is < 10ns).

Changelog from v1

Patch1:
v2: unify nsec_base (Radim)

Patch2:
v2: improve documentation (Radim)
change hypercall name to KVM_HC_CLOCK_PAIRING (Radim) increase padding size

Patch3:
v2: check for kvmclock (Radim)
initialize global variables before device registration (Radim)

author
#1 lore raw

PATCH 1/3 KVM: x86: provide realtime host clock via vsyscall notifiers

Expose the realtime host clock and save the TSC value used for the clock calculation.

Signed-off-by Marcelo Tosatti <[email protected]>
---
 arch/x86/kvm/x86.c |   36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

v2: unify nsec_base (Radim)

arch/x86/kvm/x86.c +36 -0
Index: kvm-ptpdriver/arch/x86/kvm/x86.c
===================================================================
@@ -1139,6 +1139,7 @@
 
 	u64		boot_ns;
 	u64		nsec_base;
+	u64		wall_time_sec;
 };
 
 static struct pvclock_gtod_data pvclock_gtod_data;

@@ -1162,6 +1163,8 @@
 	vdata->boot_ns			= boot_ns;
 	vdata->nsec_base		= tk->tkr_mono.xtime_nsec;
 
+	vdata->wall_time_sec            = tk->xtime_sec;
+
 	write_seqcount_end(&vdata->seq);
 }
 #endif

@@ -1623,6 +1626,28 @@
 	return mode;
 }
 
+static int do_realtime(struct timespec *ts, cycle_t *cycle_now)
+{
+	struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
+	unsigned long seq;
+	int mode;
+	u64 ns;
+
+	do {
+		seq = read_seqcount_begin(&gtod->seq);
+		mode = gtod->clock.vclock_mode;
+		ts->tv_sec = gtod->wall_time_sec;
+		ns = gtod->nsec_base;
+		ns += vgettsc(cycle_now);
+		ns >>= gtod->clock.shift;
+	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
+
+	ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
+	ts->tv_nsec = ns;
+
+	return mode;
+}
+
 /* returns true if host is using tsc clocksource */
 static bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now)
 {

@@ -1632,6 +1657,17 @@
 
 	return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;
 }
+
+/* returns true if host is using tsc clocksource */
+static bool kvm_get_walltime_and_clockread(struct timespec *ts,
+					   cycle_t *cycle_now)
+{
+	/* checked again under seqlock below */
+	if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
+		return false;
+
+	return do_realtime(ts, cycle_now) == VCLOCK_TSC;
+}
 #endif
 
 /*
author
#2 lore raw

PATCH 2/3 KVM: x86: add KVM_HC_CLOCK_OFFSET hypercall

In reply to Marcelo Tosatti

Add a hypercall to retrieve the host realtime clock and the TSC value used to calculate that clock read.

Used to implement clock synchronization between
host and guest.

Signed-off-by Marcelo Tosatti <[email protected]>
---
 Documentation/virtual/kvm/hypercalls.txt |   33 ++++++++++++++++++++++++
 arch/x86/include/uapi/asm/kvm_para.h     |    9 ++++++
 arch/x86/kvm/x86.c                       |   41 +++++++++++++++++++++++++++++++
 include/uapi/linux/kvm_para.h            |    3 ++
 4 files changed, 86 insertions(+)

v2: improve documentation (Radim)
change hypercall name to KVM_HC_CLOCK_PAIRING (Radim) increase padding size

arch/x86/include/uapi/asm/kvm_para.h +9 -0
Index: kvm-ptpdriver/arch/x86/include/uapi/asm/kvm_para.h
===================================================================
@@ -50,6 +50,15 @@
 	__u32 pad[11];
 };
 
+#define KVM_CLOCK_PAIRING_WALLCLOCK 0
+struct kvm_clock_offset {
+	__s64 sec;
+	__s64 nsec;
+	__u64 tsc;
+	__u32 flags;
+	__u32 pad[9];
+};
+
 #define KVM_STEAL_ALIGNMENT_BITS 5
 #define KVM_STEAL_VALID_BITS ((-1ULL << (KVM_STEAL_ALIGNMENT_BITS + 1)))
 #define KVM_STEAL_RESERVED_MASK (((1 << KVM_STEAL_ALIGNMENT_BITS) - 1 ) << 1)
Documentation/virtual/kvm/hypercalls.txt +33 -0
Index: kvm-ptpdriver/Documentation/virtual/kvm/hypercalls.txt
===================================================================
@@ -81,3 +81,36 @@
 same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
 specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
 is used in the hypercall for future use.
+
+
+6. KVM_HC_CLOCK_PAIRING
+------------------------
+Architecture: x86
+Status: active
+Purpose: Hypercall used to synchronize host and guest clocks.
+Usage:
+
+a0: guest physical address where host copies
+"struct kvm_clock_offset" structure.
+
+a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)
+is supported (hosts CLOCK_REALTIME clock).
+
+		struct kvm_clock_offset {
+			__s64 sec;
+			__s64 nsec;
+			__u64 tsc;
+			__u32 flags;
+			__u32 pad[9];
+		};
+
+       Where:
+               * sec: seconds from clock_type clock.
+               * nsec: nanoseconds from clock_type clock.
+               * tsc: TSC value used to calculate sec/nsec pair
+                 (this hypercall only works when host uses TSC clocksource).
+               * flags: flags, unused (0) at the moment.
+
+Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource,
+or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.
+
arch/x86/kvm/x86.c +41 -0

53 lines not on this page · raw message

include/uapi/linux/kvm_para.h +3 -0
Index: kvm-ptpdriver/include/uapi/linux/kvm_para.h
===================================================================
@@ -14,6 +14,8 @@
 #define KVM_EFAULT		EFAULT
 #define KVM_E2BIG		E2BIG
 #define KVM_EPERM		EPERM
+#define KVM_EOPNOTSUPP		EOPNOTSUPP
+#define KVM_ENOMEM		ENOMEM
 
 #define KVM_HC_VAPIC_POLL_IRQ		1
 #define KVM_HC_MMU_OP			2

@@ -23,6 +25,7 @@
 #define KVM_HC_MIPS_GET_CLOCK_FREQ	6
 #define KVM_HC_MIPS_EXIT_VM		7
 #define KVM_HC_MIPS_CONSOLE_OUTPUT	8
+#define KVM_HC_CLOCK_PAIRING		9
 
 /*
  * hypercalls use architecture specific
author
#3 lore raw

PATCH 3/3 PTP: add kvm PTP driver

In reply to Marcelo Tosatti

Add a driver with gettime method returning hosts realtime clock. This allows Chrony to synchronize host and guest clocks with high precision (see results below).

chronyc> sources
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
#* PHC0 0 3 377 6 +4ns[ +4ns] +/- 3ns

To configure Chronyd to use PHC refclock, add the
following line to its configuration file:

refclock PHC /dev/ptpX poll 3 dpoll -2 offset 0

Where /dev/ptpX is the kvmclock PTP clock.

Signed-off-by Marcelo Tosatti <[email protected]>
---
 drivers/ptp/Kconfig   |   12 +++
 drivers/ptp/Makefile  |    1 
 drivers/ptp/ptp_kvm.c |  179 ++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 192 insertions(+)

v2: check for kvmclock (Radim)
initialize global variables before device registration (Radim)

drivers/ptp/Kconfig +12 -0
Index: kvm-ptpdriver/drivers/ptp/Kconfig
===================================================================
@@ -90,4 +90,16 @@
 	  To compile this driver as a module, choose M here: the module
 	  will be called ptp_pch.
 
+config PTP_1588_CLOCK_KVM
+	tristate "KVM virtual PTP clock"
+	depends on PTP_1588_CLOCK
+	depends on KVM_GUEST
+	default y
+	help
+	  This driver adds support for using kvm infrastructure as a PTP
+	  clock. This clock is only useful if you are using KVM guests.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called ptp_kvm.
+
 endmenu
drivers/ptp/ptp_kvm.c new file +179 -0

179 lines not on this page · raw message

drivers/ptp/Makefile +1 -0
Index: kvm-ptpdriver/drivers/ptp/Makefile
===================================================================
@@ -6,3 +6,4 @@
 obj-$(CONFIG_PTP_1588_CLOCK)		+= ptp.o
 obj-$(CONFIG_PTP_1588_CLOCK_IXP46X)	+= ptp_ixp46x.o
 obj-$(CONFIG_PTP_1588_CLOCK_PCH)	+= ptp_pch.o
+obj-$(CONFIG_PTP_1588_CLOCK_KVM)	+= ptp_kvm.o