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authorGlauber de Oliveira Costa <gcosta@redhat.com>2008-02-15 22:52:48 +0300
committerAvi Kivity <avi@qumranet.com>2008-04-27 12:53:22 +0400
commit790c73f6289a204f858ffdcbe4a2b38e91657ec6 (patch)
tree3d6b146538b11e45a713bb4fa1b44af4509ca27f /arch/x86/kernel/kvmclock.c
parent18068523d3a0b41fcee5b53cdb437a0ab4d65e4b (diff)
downloadlinux-790c73f6289a204f858ffdcbe4a2b38e91657ec6.tar.xz
x86: KVM guest: paravirtualized clocksource
This is the guest part of kvm clock implementation It does not do tsc-only timing, as tsc can have deltas between cpus, and it did not seem worthy to me to keep adjusting them. We do use it, however, for fine-grained adjustment. Other than that, time comes from the host. [randy dunlap: add missing include] [randy dunlap: disallow on Voyager or Visual WS] Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com> Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Avi Kivity <avi@qumranet.com>
Diffstat (limited to 'arch/x86/kernel/kvmclock.c')
-rw-r--r--arch/x86/kernel/kvmclock.c160
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 000000000000..b999f5e5b3bf
--- /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);
+ }
+}