KVM: x86: add KVM_HC_CLOCK_PAIRING hypercall

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.

Marcelo Tosatti committed 9 years ago

Commit 55dd00a1 parent 6342c504 files · +112 −0Browse files

Unified · Split

4 files

Documentation/virtual/kvm/hypercalls.txt +35 −0
arch/x86/include/uapi/asm/kvm_para.h +9 −0
arch/x86/kvm/x86.c +66 −0
include/uapi/linux/kvm_para.h +2 −0

Documentation/virtual/kvm/hypercalls.txt+35−0

@@ -81,3 +81,38 @@ the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the · 80 unmodified lines
81	81	same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
82	82	specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
83	83	is used in the hypercall for future use.
	84	+
	85	+
	86	+6. KVM_HC_CLOCK_PAIRING
	87	+------------------------
	88	+Architecture: x86
	89	+Status: active
	90	+Purpose: Hypercall used to synchronize host and guest clocks.
	91	+Usage:
	92	+
	93	+a0: guest physical address where host copies
	94	+"struct kvm_clock_offset" structure.
	95	+
	96	+a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)
	97	+is supported (corresponding to the host's CLOCK_REALTIME clock).
	98	+
	99	+ struct kvm_clock_pairing {
	100	+ __s64 sec;
	101	+ __s64 nsec;
	102	+ __u64 tsc;
	103	+ __u32 flags;
	104	+ __u32 pad[9];
	105	+ };
	106	+
	107	+ Where:
	108	+ * sec: seconds from clock_type clock.
	109	+ * nsec: nanoseconds from clock_type clock.
	110	+ * tsc: guest TSC value used to calculate sec/nsec pair
	111	+ * flags: flags, unused (0) at the moment.
	112	+
	113	+The hypercall lets a guest compute a precise timestamp across
	114	+host and guest. The guest can use the returned TSC value to
	115	+compute the CLOCK_REALTIME for its clock, at the same instant.
	116	+
	117	+Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource,
	118	+or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.

arch/x86/include/uapi/asm/kvm_para.h+9−0

@@ -50,6 +50,15 @@ struct kvm_steal_time { · 49 unmodified lines
50	50	__u32 pad[11];
51	51	};
52	52
	53	+#define KVM_CLOCK_PAIRING_WALLCLOCK 0
	54	+struct kvm_clock_pairing {
	55	+ __s64 sec;
	56	+ __s64 nsec;
	57	+ __u64 tsc;
	58	+ __u32 flags;
	59	+ __u32 pad[9];
	60	+};
	61	+
53	62	#define KVM_STEAL_ALIGNMENT_BITS 5
54	63	#define KVM_STEAL_VALID_BITS ((-1ULL << (KVM_STEAL_ALIGNMENT_BITS + 1)))
55	64	#define KVM_STEAL_RESERVED_MASK (((1 << KVM_STEAL_ALIGNMENT_BITS) - 1 ) << 1)

arch/x86/kvm/x86.c+66−0

@@ -1142,6 +1142,7 @@ struct pvclock_gtod_data { · 1141 unmodified lines
1142	1142
1143	1143	u64 boot_ns;
1144	1144	u64 nsec_base;
	1145	+ u64 wall_time_sec;
1145	1146	};
1146	1147
1147	1148	static struct pvclock_gtod_data pvclock_gtod_data;
@@ -1165,6 +1166,8 @@ static void update_pvclock_gtod(struct timekeeper *tk) · 17 unmodified lines
1165	1166	vdata->boot_ns = boot_ns;
1166	1167	vdata->nsec_base = tk->tkr_mono.xtime_nsec;
1167	1168
	1169	+ vdata->wall_time_sec = tk->xtime_sec;
	1170	+
1168	1171	write_seqcount_end(&vdata->seq);
1169	1172	}
1170	1173	#endif
@@ -1626,6 +1629,28 @@ static int do_monotonic_boot(s64 t, u64 cycle_now) · 455 unmodified lines
1626	1629	return mode;
1627	1630	}
1628	1631
	1632	+static int do_realtime(struct timespec ts, u64 cycle_now)
	1633	+{
	1634	+ struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
	1635	+ unsigned long seq;
	1636	+ int mode;
	1637	+ u64 ns;
	1638	+
	1639	+ do {
	1640	+ seq = read_seqcount_begin(&gtod->seq);
	1641	+ mode = gtod->clock.vclock_mode;
	1642	+ ts->tv_sec = gtod->wall_time_sec;
	1643	+ ns = gtod->nsec_base;
	1644	+ ns += vgettsc(cycle_now);
	1645	+ ns >>= gtod->clock.shift;
	1646	+ } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
	1647	+
	1648	+ ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
	1649	+ ts->tv_nsec = ns;
	1650	+
	1651	+ return mode;
	1652	+}
	1653	+
1629	1654	/* returns true if host is using tsc clocksource */
1630	1655	static bool kvm_get_time_and_clockread(s64 kernel_ns, u64 cycle_now)
1631	1656	{
@@ -1635,6 +1660,17 @@ static bool kvm_get_time_and_clockread(s64 kernel_ns, u64 cycle_now) · 3 unmodified lines
1635	1660
1636	1661	return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;
1637	1662	}
	1663	+
	1664	+/* returns true if host is using tsc clocksource */
	1665	+static bool kvm_get_walltime_and_clockread(struct timespec *ts,
	1666	+ u64 *cycle_now)
	1667	+{
	1668	+ /* checked again under seqlock below */
	1669	+ if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
	1670	+ return false;
	1671	+
	1672	+ return do_realtime(ts, cycle_now) == VCLOCK_TSC;
	1673	+}
1638	1674	#endif
1639	1675
1640	1676	/*
@@ -6112,6 +6148,33 @@ int kvm_emulate_halt(struct kvm_vcpu *vcpu) · 4471 unmodified lines
6112	6148	}
6113	6149	EXPORT_SYMBOL_GPL(kvm_emulate_halt);
6114	6150
	6151	+static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
	6152	+ unsigned long clock_type)
	6153	+{
	6154	+ struct kvm_clock_pairing clock_pairing;
	6155	+ struct timespec ts;
	6156	+ cycle_t cycle;
	6157	+ int ret;
	6158	+
	6159	+ if (clock_type != KVM_CLOCK_PAIRING_WALLCLOCK)
	6160	+ return -KVM_EOPNOTSUPP;
	6161	+
	6162	+ if (kvm_get_walltime_and_clockread(&ts, &cycle) == false)
	6163	+ return -KVM_EOPNOTSUPP;
	6164	+
	6165	+ clock_pairing.sec = ts.tv_sec;
	6166	+ clock_pairing.nsec = ts.tv_nsec;
	6167	+ clock_pairing.tsc = kvm_read_l1_tsc(vcpu, cycle);
	6168	+ clock_pairing.flags = 0;
	6169	+
	6170	+ ret = 0;
	6171	+ if (kvm_write_guest(vcpu->kvm, paddr, &clock_pairing,
	6172	+ sizeof(struct kvm_clock_pairing)))
	6173	+ ret = -KVM_EFAULT;
	6174	+
	6175	+ return ret;
	6176	+}
	6177	+
6115	6178	/*
6116	6179	* kvm_pv_kick_cpu_op: Kick a vcpu.
6117	6180	*
@@ -6176,6 +6239,9 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) · 58 unmodified lines
6176	6239	kvm_pv_kick_cpu_op(vcpu->kvm, a0, a1);
6177	6240	ret = 0;
6178	6241	break;
	6242	+ case KVM_HC_CLOCK_PAIRING:
	6243	+ ret = kvm_pv_clock_pairing(vcpu, a0, a1);
	6244	+ break;
6179	6245	default:
6180	6246	ret = -KVM_ENOSYS;
6181	6247	break;

include/uapi/linux/kvm_para.h+2−0

@@ -14,6 +14,7 @@ · 13 unmodified lines
14	14	#define KVM_EFAULT EFAULT
15	15	#define KVM_E2BIG E2BIG
16	16	#define KVM_EPERM EPERM
	17	+#define KVM_EOPNOTSUPP 95
17	18
18	19	#define KVM_HC_VAPIC_POLL_IRQ 1
19	20	#define KVM_HC_MMU_OP 2
@@ -23,6 +24,7 @@ · 3 unmodified lines
23	24	#define KVM_HC_MIPS_GET_CLOCK_FREQ 6
24	25	#define KVM_HC_MIPS_EXIT_VM 7
25	26	#define KVM_HC_MIPS_CONSOLE_OUTPUT 8
	27	+#define KVM_HC_CLOCK_PAIRING 9
26	28
27	29	/*
28	30	* hypercalls use architecture specific

KVM: x86: add KVM_HC_CLOCK_PAIRING hypercall

Keyboard shortcuts

General

Issues and pull requests

Issues, pull requests and Inbox

Repository code