[patch 2/3] KVM: x86: add KVM_HC_CLOCK_OFFSET hypercall

[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 <mtosatti@xxxxxxxxxx>

---
 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

Index: kvm-ptpdriver/arch/x86/include/uapi/asm/kvm_para.h
===================================================================
--- kvm-ptpdriver.orig/arch/x86/include/uapi/asm/kvm_para.h	2017-01-13 15:43:47.196867691 -0200
+++ kvm-ptpdriver/arch/x86/include/uapi/asm/kvm_para.h	2017-01-13 15:59:39.596193853 -0200
@@ -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)
Index: kvm-ptpdriver/Documentation/virtual/kvm/hypercalls.txt
===================================================================
--- kvm-ptpdriver.orig/Documentation/virtual/kvm/hypercalls.txt	2017-01-13 15:43:47.196867691 -0200
+++ kvm-ptpdriver/Documentation/virtual/kvm/hypercalls.txt	2017-01-13 15:59:26.676163231 -0200
@@ -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.
+
Index: kvm-ptpdriver/arch/x86/kvm/x86.c
===================================================================
--- kvm-ptpdriver.orig/arch/x86/kvm/x86.c	2017-01-13 15:49:14.058347822 -0200
+++ kvm-ptpdriver/arch/x86/kvm/x86.c	2017-01-13 16:00:56.964373208 -0200
@@ -6119,6 +6119,44 @@
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_halt);
 
+static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
+			       unsigned long clock_type)
+{
+	struct kvm_clock_offset *clock_offset;
+	struct timespec ts;
+	cycle_t cycle;
+	int ret;
+
+	if (clock_type != KVM_CLOCK_PAIRING_WALLCLOCK)
+		return -KVM_EOPNOTSUPP;
+
+	if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
+		return -KVM_EOPNOTSUPP;
+
+	clock_offset = kzalloc(sizeof(struct kvm_clock_offset), GFP_KERNEL);
+	if (clock_offset == NULL)
+		return -KVM_ENOMEM;
+
+	if (kvm_get_walltime_and_clockread(&ts, &cycle) == false) {
+		kfree(clock_offset);
+		return -KVM_EOPNOTSUPP;
+	}
+
+	clock_offset->sec = ts.tv_sec;
+	clock_offset->nsec = ts.tv_nsec;
+	clock_offset->tsc = kvm_read_l1_tsc(vcpu, cycle);
+	clock_offset->flags = 0;
+
+	ret = 0;
+	if (kvm_write_guest(vcpu->kvm, paddr, clock_offset,
+			      sizeof(struct kvm_clock_offset)))
+		ret = -KVM_EFAULT;
+
+	kfree(clock_offset);
+
+	return ret;
+}
+
 /*
  * kvm_pv_kick_cpu_op:  Kick a vcpu.
  *
@@ -6183,6 +6221,9 @@
 		kvm_pv_kick_cpu_op(vcpu->kvm, a0, a1);
 		ret = 0;
 		break;
+	case KVM_HC_CLOCK_PAIRING:
+		ret = kvm_pv_clock_pairing(vcpu, a0, a1);
+		break;
 	default:
 		ret = -KVM_ENOSYS;
 		break;
Index: kvm-ptpdriver/include/uapi/linux/kvm_para.h
===================================================================
--- kvm-ptpdriver.orig/include/uapi/linux/kvm_para.h	2017-01-13 15:43:47.196867691 -0200
+++ kvm-ptpdriver/include/uapi/linux/kvm_para.h	2017-01-13 16:01:09.290401187 -0200
@@ -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