Commit 790c73f6 authored by Glauber de Oliveira Costa's avatar Glauber de Oliveira Costa Committed by Avi Kivity

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: default avatarGlauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: default avatarRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent 18068523
......@@ -373,6 +373,17 @@ 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
depends on !(X86_VISWS || X86_VOYAGER)
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 such as time of day, and
system time
source "arch/x86/lguest/Kconfig"
config PARAVIRT
......
......@@ -80,6 +80,7 @@ obj-$(CONFIG_DEBUG_RODATA_TEST) += test_rodata.o
obj-$(CONFIG_DEBUG_NX_TEST) += test_nx.o
obj-$(CONFIG_VMI) += vmi_32.o vmiclock_32.o
obj-$(CONFIG_KVM_CLOCK) += kvmclock.o
obj-$(CONFIG_PARAVIRT) += paravirt.o paravirt_patch_$(BITS).o
ifdef CONFIG_INPUT_PCSPKR
......
/* 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);
}
}
......@@ -47,6 +47,7 @@
#include <linux/pfn.h>
#include <linux/pci.h>
#include <linux/init_ohci1394_dma.h>
#include <linux/kvm_para.h>
#include <video/edid.h>
......@@ -820,6 +821,10 @@ 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
......
......@@ -42,6 +42,7 @@
#include <linux/ctype.h>
#include <linux/uaccess.h>
#include <linux/init_ohci1394_dma.h>
#include <linux/kvm_para.h>
#include <asm/mtrr.h>
#include <asm/uaccess.h>
......@@ -384,6 +385,10 @@ void __init setup_arch(char **cmdline_p)
io_delay_init();
#ifdef CONFIG_KVM_CLOCK
kvmclock_init();
#endif
#ifdef CONFIG_SMP
/* setup to use the early static init tables during kernel startup */
x86_cpu_to_apicid_early_ptr = (void *)x86_cpu_to_apicid_init;
......
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