1 /* KVM paravirtual clock driver. A clocksource implementation
2 Copyright (C) 2008 Glauber de Oliveira Costa, Red Hat Inc.
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 2 of the License, or
7 (at your option) any later version.
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
14 You should have received a copy of the GNU General Public License
15 along with this program; if not, write to the Free Software
16 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
19 #include <linux/clocksource.h>
20 #include <linux/kvm_para.h>
21 #include <asm/arch_hooks.h>
24 #include <linux/percpu.h>
28 static int kvmclock = 1;
30 static int parse_no_kvmclock(char *arg)
35 early_param("no-kvmclock", parse_no_kvmclock);
37 /* The hypervisor will put information about time periodically here */
38 static DEFINE_PER_CPU_SHARED_ALIGNED(struct kvm_vcpu_time_info, hv_clock);
39 #define get_clock(cpu, field) per_cpu(hv_clock, cpu).field
41 static inline u64 kvm_get_delta(u64 last_tsc)
43 int cpu = smp_processor_id();
44 u64 delta = native_read_tsc() - last_tsc;
45 return (delta * get_clock(cpu, tsc_to_system_mul)) >> KVM_SCALE;
48 static struct kvm_wall_clock wall_clock;
49 static cycle_t kvm_clock_read(void);
51 * The wallclock is the time of day when we booted. Since then, some time may
52 * have elapsed since the hypervisor wrote the data. So we try to account for
53 * that with system time
55 unsigned long kvm_get_wallclock(void)
63 low = (int)__pa(&wall_clock);
64 high = ((u64)__pa(&wall_clock) >> 32);
66 delta = kvm_clock_read();
68 native_write_msr(MSR_KVM_WALL_CLOCK, low, high);
70 version = wall_clock.wc_version;
72 wc_sec = wall_clock.wc_sec;
73 wc_nsec = wall_clock.wc_nsec;
75 } while ((wall_clock.wc_version != version) || (version & 1));
77 delta = kvm_clock_read() - delta;
79 nsec = do_div(delta, NSEC_PER_SEC);
80 set_normalized_timespec(&ts, wc_sec + delta, nsec);
82 * Of all mechanisms of time adjustment I've tested, this one
88 int kvm_set_wallclock(unsigned long now)
94 * This is our read_clock function. The host puts an tsc timestamp each time
95 * it updates a new time. Without the tsc adjustment, we can have a situation
96 * in which a vcpu starts to run earlier (smaller system_time), but probes
97 * time later (compared to another vcpu), leading to backwards time
99 static cycle_t kvm_clock_read(void)
105 cpu = smp_processor_id();
107 last_tsc = get_clock(cpu, tsc_timestamp);
108 now = get_clock(cpu, system_time);
110 now += kvm_get_delta(last_tsc);
115 static struct clocksource kvm_clock = {
117 .read = kvm_clock_read,
119 .mask = CLOCKSOURCE_MASK(64),
120 .mult = 1 << KVM_SCALE,
122 .flags = CLOCK_SOURCE_IS_CONTINUOUS,
125 static int kvm_register_clock(void)
127 int cpu = smp_processor_id();
129 low = (int)__pa(&per_cpu(hv_clock, cpu)) | 1;
130 high = ((u64)__pa(&per_cpu(hv_clock, cpu)) >> 32);
132 return native_write_msr_safe(MSR_KVM_SYSTEM_TIME, low, high);
135 static void kvm_setup_secondary_clock(void)
138 * Now that the first cpu already had this clocksource initialized,
141 WARN_ON(kvm_register_clock());
142 /* ok, done with our trickery, call native */
143 setup_secondary_APIC_clock();
146 void __init kvmclock_init(void)
148 if (!kvm_para_available())
151 if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
152 if (kvm_register_clock())
154 pv_time_ops.get_wallclock = kvm_get_wallclock;
155 pv_time_ops.set_wallclock = kvm_set_wallclock;
156 pv_time_ops.sched_clock = kvm_clock_read;
157 pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock;
158 clocksource_register(&kvm_clock);