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Diffstat (limited to 'arch/x86/kernel/kvmclock.c')
| -rw-r--r-- | arch/x86/kernel/kvmclock.c | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c new file mode 100644 index 00000000000..b999f5e5b3b --- /dev/null +++ b/arch/x86/kernel/kvmclock.c @@ -0,0 +1,160 @@ +/* KVM paravirtual clock driver. A clocksource implementation + Copyright (C) 2008 Glauber de Oliveira Costa, Red Hat Inc. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA +*/ + +#include <linux/clocksource.h> +#include <linux/kvm_para.h> +#include <asm/arch_hooks.h> +#include <asm/msr.h> +#include <asm/apic.h> +#include <linux/percpu.h> + +#define KVM_SCALE 22 + +static int kvmclock = 1; + +static int parse_no_kvmclock(char *arg) +{ + kvmclock = 0; + return 0; +} +early_param("no-kvmclock", parse_no_kvmclock); + +/* The hypervisor will put information about time periodically here */ +static DEFINE_PER_CPU_SHARED_ALIGNED(struct kvm_vcpu_time_info, hv_clock); +#define get_clock(cpu, field) per_cpu(hv_clock, cpu).field + +static inline u64 kvm_get_delta(u64 last_tsc) +{ + int cpu = smp_processor_id(); + u64 delta = native_read_tsc() - last_tsc; + return (delta * get_clock(cpu, tsc_to_system_mul)) >> KVM_SCALE; +} + +static struct kvm_wall_clock wall_clock; +static cycle_t kvm_clock_read(void); +/* + * The wallclock is the time of day when we booted. Since then, some time may + * have elapsed since the hypervisor wrote the data. So we try to account for + * that with system time + */ +unsigned long kvm_get_wallclock(void) +{ + u32 wc_sec, wc_nsec; + u64 delta; + struct timespec ts; + int version, nsec; + int low, high; + + low = (int)__pa(&wall_clock); + high = ((u64)__pa(&wall_clock) >> 32); + + delta = kvm_clock_read(); + + native_write_msr(MSR_KVM_WALL_CLOCK, low, high); + do { + version = wall_clock.wc_version; + rmb(); + wc_sec = wall_clock.wc_sec; + wc_nsec = wall_clock.wc_nsec; + rmb(); + } while ((wall_clock.wc_version != version) || (version & 1)); + + delta = kvm_clock_read() - delta; + delta += wc_nsec; + nsec = do_div(delta, NSEC_PER_SEC); + set_normalized_timespec(&ts, wc_sec + delta, nsec); + /* + * Of all mechanisms of time adjustment I've tested, this one + * was the champion! + */ + return ts.tv_sec + 1; +} + +int kvm_set_wallclock(unsigned long now) +{ + return 0; +} + +/* + * This is our read_clock function. The host puts an tsc timestamp each time + * it updates a new time. Without the tsc adjustment, we can have a situation + * in which a vcpu starts to run earlier (smaller system_time), but probes + * time later (compared to another vcpu), leading to backwards time + */ +static cycle_t kvm_clock_read(void) +{ + u64 last_tsc, now; + int cpu; + + preempt_disable(); + cpu = smp_processor_id(); + + last_tsc = get_clock(cpu, tsc_timestamp); + now = get_clock(cpu, system_time); + + now += kvm_get_delta(last_tsc); + preempt_enable(); + + return now; +} +static struct clocksource kvm_clock = { + .name = "kvm-clock", + .read = kvm_clock_read, + .rating = 400, + .mask = CLOCKSOURCE_MASK(64), + .mult = 1 << KVM_SCALE, + .shift = KVM_SCALE, + .flags = CLOCK_SOURCE_IS_CONTINUOUS, +}; + +static int kvm_register_clock(void) +{ + int cpu = smp_processor_id(); + int low, high; + low = (int)__pa(&per_cpu(hv_clock, cpu)) | 1; + high = ((u64)__pa(&per_cpu(hv_clock, cpu)) >> 32); + + return native_write_msr_safe(MSR_KVM_SYSTEM_TIME, low, high); +} + +static void kvm_setup_secondary_clock(void) +{ + /* + * Now that the first cpu already had this clocksource initialized, + * we shouldn't fail. + */ + WARN_ON(kvm_register_clock()); + /* ok, done with our trickery, call native */ + setup_secondary_APIC_clock(); +} + +void __init kvmclock_init(void) +{ + if (!kvm_para_available()) + return; + + if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) { + if (kvm_register_clock()) + return; + pv_time_ops.get_wallclock = kvm_get_wallclock; + pv_time_ops.set_wallclock = kvm_set_wallclock; + pv_time_ops.sched_clock = kvm_clock_read; + pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock; + clocksource_register(&kvm_clock); + } +} |