arch/x86/kernel/kvmclock.c

   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 #ifdef CONFIG_X86_LOCAL_APIC
 137 static void kvm_setup_secondary_clock(void)
 138 {
 139         /*
 140          * Now that the first cpu already had this clocksource initialized,
 141          * we shouldn't fail.
 142          */
 143         WARN_ON(kvm_register_clock());
 144         /* ok, done with our trickery, call native */
 145         setup_secondary_APIC_clock();
 146 }
 147 #endif
 148
 149 /*
 150  * After the clock is registered, the host will keep writing to the
 151  * registered memory location. If the guest happens to shutdown, this memory
 152  * won't be valid. In cases like kexec, in which you install a new kernel, this
 153  * means a random memory location will be kept being written. So before any
 154  * kind of shutdown from our side, we unregister the clock by writting anything
 155  * that does not have the 'enable' bit set in the msr
 156  */
 157 #ifdef CONFIG_KEXEC
 158 static void kvm_crash_shutdown(struct pt_regs *regs)
 159 {
 160         native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0);
 161         native_machine_crash_shutdown(regs);
 162 }
 163 #endif
 164
 165 static void kvm_shutdown(void)
 166 {
 167         native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0);
 168         native_machine_shutdown();
 169 }
 170
 171 void __init kvmclock_init(void)
 172 {
 173         if (!kvm_para_available())
 174                 return;
 175
 176         if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
 177                 if (kvm_register_clock())
 178                         return;
 179                 pv_time_ops.get_wallclock = kvm_get_wallclock;
 180                 pv_time_ops.set_wallclock = kvm_set_wallclock;
 181                 pv_time_ops.sched_clock = kvm_clock_read;
 182 #ifdef CONFIG_X86_LOCAL_APIC
 183                 pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock;
 184 #endif
 185                 machine_ops.shutdown  = kvm_shutdown;
 186 #ifdef CONFIG_KEXEC
 187                 machine_ops.crash_shutdown  = kvm_crash_shutdown;
 188 #endif
 189                 clocksource_register(&kvm_clock);
 190         }
 191 }