1 /* KVM paravirtual clock driver. A clocksource implementation 2 Copyright (C) 2008 Glauber de Oliveira Costa, Red Hat Inc. 3 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. 8 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. 13 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 17 */ 18 19 #include <linux/clocksource.h> 20 #include <linux/kvm_para.h> 21 #include <asm/arch_hooks.h> 22 #include <asm/msr.h> 23 #include <asm/apic.h> 24 #include <linux/percpu.h> 25 #include <asm/reboot.h> 26 27 #define KVM_SCALE 22 28 29 static int kvmclock = 1; 30 31 static int parse_no_kvmclock(char *arg) 32 { 33 kvmclock = 0; 34 return 0; 35 } 36 early_param("no-kvmclock", parse_no_kvmclock); 37 38 /* The hypervisor will put information about time periodically here */ 39 static DEFINE_PER_CPU_SHARED_ALIGNED(struct kvm_vcpu_time_info, hv_clock); 40 #define get_clock(cpu, field) per_cpu(hv_clock, cpu).field 41 42 static inline u64 kvm_get_delta(u64 last_tsc) 43 { 44 int cpu = smp_processor_id(); 45 u64 delta = native_read_tsc() - last_tsc; 46 return (delta * get_clock(cpu, tsc_to_system_mul)) >> KVM_SCALE; 47 } 48 49 static struct kvm_wall_clock wall_clock; 50 static cycle_t kvm_clock_read(void); 51 /* 52 * The wallclock is the time of day when we booted. Since then, some time may 53 * have elapsed since the hypervisor wrote the data. So we try to account for 54 * that with system time 55 */ 56 unsigned long kvm_get_wallclock(void) 57 { 58 u32 wc_sec, wc_nsec; 59 u64 delta; 60 struct timespec ts; 61 int version, nsec; 62 int low, high; 63 64 low = (int)__pa(&wall_clock); 65 high = ((u64)__pa(&wall_clock) >> 32); 66 67 delta = kvm_clock_read(); 68 69 native_write_msr(MSR_KVM_WALL_CLOCK, low, high); 70 do { 71 version = wall_clock.wc_version; 72 rmb(); 73 wc_sec = wall_clock.wc_sec; 74 wc_nsec = wall_clock.wc_nsec; 75 rmb(); 76 } while ((wall_clock.wc_version != version) || (version & 1)); 77 78 delta = kvm_clock_read() - delta; 79 delta += wc_nsec; 80 nsec = do_div(delta, NSEC_PER_SEC); 81 set_normalized_timespec(&ts, wc_sec + delta, nsec); 82 /* 83 * Of all mechanisms of time adjustment I've tested, this one 84 * was the champion! 85 */ 86 return ts.tv_sec + 1; 87 } 88 89 int kvm_set_wallclock(unsigned long now) 90 { 91 return 0; 92 } 93 94 /* 95 * This is our read_clock function. The host puts an tsc timestamp each time 96 * it updates a new time. Without the tsc adjustment, we can have a situation 97 * in which a vcpu starts to run earlier (smaller system_time), but probes 98 * time later (compared to another vcpu), leading to backwards time 99 */ 100 static cycle_t kvm_clock_read(void) 101 { 102 u64 last_tsc, now; 103 int cpu; 104 105 preempt_disable(); 106 cpu = smp_processor_id(); 107 108 last_tsc = get_clock(cpu, tsc_timestamp); 109 now = get_clock(cpu, system_time); 110 111 now += kvm_get_delta(last_tsc); 112 preempt_enable(); 113 114 return now; 115 } 116 static struct clocksource kvm_clock = { 117 .name = "kvm-clock", 118 .read = kvm_clock_read, 119 .rating = 400, 120 .mask = CLOCKSOURCE_MASK(64), 121 .mult = 1 << KVM_SCALE, 122 .shift = KVM_SCALE, 123 .flags = CLOCK_SOURCE_IS_CONTINUOUS, 124 }; 125 126 static int kvm_register_clock(void) 127 { 128 int cpu = smp_processor_id(); 129 int low, high; 130 low = (int)__pa(&per_cpu(hv_clock, cpu)) | 1; 131 high = ((u64)__pa(&per_cpu(hv_clock, cpu)) >> 32); 132 133 return native_write_msr_safe(MSR_KVM_SYSTEM_TIME, low, high); 134 } 135 136 static void kvm_setup_secondary_clock(void) 137 { 138 /* 139 * Now that the first cpu already had this clocksource initialized, 140 * we shouldn't fail. 141 */ 142 WARN_ON(kvm_register_clock()); 143 /* ok, done with our trickery, call native */ 144 setup_secondary_APIC_clock(); 145 } 146 147 /* 148 * After the clock is registered, the host will keep writing to the 149 * registered memory location. If the guest happens to shutdown, this memory 150 * won't be valid. In cases like kexec, in which you install a new kernel, this 151 * means a random memory location will be kept being written. So before any 152 * kind of shutdown from our side, we unregister the clock by writting anything 153 * that does not have the 'enable' bit set in the msr 154 */ 155 #ifdef CONFIG_KEXEC 156 static void kvm_crash_shutdown(struct pt_regs *regs) 157 { 158 native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0); 159 native_machine_crash_shutdown(regs); 160 } 161 #endif 162 163 static void kvm_shutdown(void) 164 { 165 native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0); 166 native_machine_shutdown(); 167 } 168 169 void __init kvmclock_init(void) 170 { 171 if (!kvm_para_available()) 172 return; 173 174 if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) { 175 if (kvm_register_clock()) 176 return; 177 pv_time_ops.get_wallclock = kvm_get_wallclock; 178 pv_time_ops.set_wallclock = kvm_set_wallclock; 179 pv_time_ops.sched_clock = kvm_clock_read; 180 pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock; 181 machine_ops.shutdown = kvm_shutdown; 182 #ifdef CONFIG_KEXEC 183 machine_ops.crash_shutdown = kvm_crash_shutdown; 184 #endif 185 clocksource_register(&kvm_clock); 186 } 187 } 188