[PATCH 3/3] kvmclock implementation, the guest part.

Glauber de Oliveira Costa
2007-11-08T21:39:25Z

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.

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
---
arch/x86/Kconfig.i386 | 10 +++
arch/x86/kernel/Makefile_32 | 1 +
arch/x86/kernel/kvmclock.c | 171 +++++++++++++++++++++++++++++++++++++++++++
arch/x86/kernel/setup_32.c | 5 +
4 files changed, 187 insertions(+), 0 deletions(-)
create mode 100644 arch/x86/kernel/kvmclock.c

diff --git a/arch/x86/Kconfig.i386 b/arch/x86/Kconfig.i386
index 7331efe..5fe4025 100644
--- a/arch/x86/Kconfig.i386
+++ b/arch/x86/Kconfig.i386
@@ -257,6 +257,16 @@ config VMI
at the moment), by linking the kernel to a GPL-ed ROM module
provided by the hypervisor.

+config KVM_CLOCK
+ bool "KVM paravirtualized clock"
+ select PARAVIRT
+ help
+ Turning on this option will allow you to run a paravirtualized clock
+ when running over the KVM hypervisor. Instead of relying on a PIT
+ (or probably other) emulation by the underlying device model, the host
+ provides the guest with timing infrastructure, as time of day, and
+ timer expiration.
+
source "arch/x86/lguest/Kconfig"

endif
diff --git a/arch/x86/kernel/Makefile_32 b/arch/x86/kernel/Makefile_32
index b9d6798..df76d8c 100644
--- a/arch/x86/kernel/Makefile_32
+++ b/arch/x86/kernel/Makefile_32
@@ -43,6 +43,7 @@ obj-$(CONFIG_K8_NB) += k8.o
obj-$(CONFIG_MGEODE_LX) += geode_32.o mfgpt_32.o

obj-$(CONFIG_VMI) += vmi_32.o vmiclock_32.o
+obj-$(CONFIG_KVM_CLOCK) += kvmclock.o
obj-$(CONFIG_PARAVIRT) += paravirt_32.o
obj-y += pcspeaker.o

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
new file mode 100644
index 0000000..df14613
--- /dev/null
+++ b/arch/x86/kernel/kvmclock.c
@@ -0,0 +1,171 @@
+/* KVM paravirtual clock driver. A clocksource implementation
+ Copyright (C) 2007 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/clockchips.h>
+#include <linux/interrupt.h>
+#include <linux/kvm_para.h>
+#include <linux/ktime.h>
+#include <asm/arch_hooks.h>
+#include <asm/i8253.h>
+
+#include <mach_ipi.h>
+#include <irq_vectors.h>
+
+#define KVM_SCALE 22
+
+#define get_clock(cpu, field) hv_clock[cpu].fields.field
+
+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 */
+union kvm_hv_clock hv_clock[NR_CPUS] __attribute__((__aligned__(PAGE_SIZE)));
+
+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_mult)) >> KVM_SCALE;
+}
+
+/*
+ * 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. Even if the tsc is not accurate, it gives us a more accurate timing
+ * than not adjusting at all
+ */
+unsigned long kvm_get_wallclock(void)
+{
+ u64 wc_sec, delta, last_tsc;
+ struct timespec ts;
+ int version, nsec, cpu = smp_processor_id();
+
+ do {
+ version = get_clock(cpu, version);
+ rmb();
+ last_tsc = get_clock(cpu, last_tsc);
+ rmb();
+ wc_sec = get_clock(cpu, wc_sec);
+ rmb();
+ } while ((get_clock(cpu, version) != version) && !(version & 1));
+
+ delta = kvm_get_delta(last_tsc);
+ 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, and then we can use it to derive a slightly more
+ * precise notion of elapsed time, converted to nanoseconds.
+ */
+static cycle_t kvm_clock_read(void)
+{
+
+ u64 last_tsc, now;
+ u32 version;
+ int cpu = smp_processor_id();
+
+ do {
+ version = get_clock(cpu, version);
+ rmb();
+ last_tsc = get_clock(cpu, last_tsc);
+ rmb();
+ now = get_clock(cpu, now_ns);
+ rmb();
+ } while ((get_clock(cpu, version) != version) && !(version & 1));
+
+ return now + kvm_get_delta(last_tsc);
+}
+
+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,
+};
+
+unsigned long long kvm_sched_clock(void)
+{
+ return kvm_clock_read();
+}
+
+static int kvm_register_clock(unsigned int cpu)
+{
+ unsigned long kvm_clock_info = __pa((unsigned long)&hv_clock[cpu]);
+ kvm_clock_info >>= PAGE_SHIFT; /* page frame number */
+ return kvm_hypercall1(KVM_HCALL_REGISTER_CLOCK, kvm_clock_info);
+}
+
+void kvm_setup_secondary_clock(void)
+{
+ /*
+ * Now that the first cpu already had this clocksource initialized,
+ * we shouldn't fail.
+ */
+ int cpu = smp_processor_id();
+ WARN_ON(kvm_register_clock(cpu));
+ /* ok, done with our trickery, call native */
+ setup_secondary_APIC_clock();
+}
+
+void __init kvmclock_init(void)
+{
+ int cpu = smp_processor_id();
+ int r;
+
+ /*
+ * If we can't use the paravirt clock, just go with
+ * the usual timekeeping
+ */
+ if (!kvm_para_available())
+ return;
+
+ r = kvm_register_clock(cpu);
+ if (r)
+ return;
+
+ if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
+ pv_time_ops.get_wallclock = kvm_get_wallclock;
+ pv_time_ops.set_wallclock = kvm_set_wallclock;
+ pv_time_ops.sched_clock = kvm_sched_clock;
+ pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock;
+ clocksource_register(&kvm_clock);
+ }
+}
diff --git a/arch/x86/kernel/setup_32.c b/arch/x86/kernel/setup_32.c
index e1e18c3..9f13ff6 100644
--- a/arch/x86/kernel/setup_32.c
+++ b/arch/x86/kernel/setup_32.c
@@ -44,6 +44,7 @@
#include <linux/crash_dump.h>
#include <linux/dmi.h>
#include <linux/pfn.h>
+#include <linux/kvm_para.h>

#include <video/edid.h>

@@ -614,6 +615,10 @@ void __init setup_arch(char **cmdline_p)

max_low_pfn = setup_memory();

+#ifdef CONFIG_KVM_CLOCK
+ kvmclock_init();
+#endif
+
#ifdef CONFIG_VMI
/*
* Must be after max_low_pfn is determined, and before kernel
--
1.5.0.6