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    Subject[PATCH 33/40] x86: KVM guest: paravirtualized clocksource
    Date
    From: Glauber de Oliveira Costa <gcosta@redhat.com>

    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>
    ---
    arch/x86/Kconfig | 11 +++
    arch/x86/kernel/Makefile | 1 +
    arch/x86/kernel/kvmclock.c | 160 ++++++++++++++++++++++++++++++++++++++++++++
    arch/x86/kernel/setup_32.c | 5 ++
    arch/x86/kernel/setup_64.c | 5 ++
    5 files changed, 182 insertions(+), 0 deletions(-)
    create mode 100644 arch/x86/kernel/kvmclock.c

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index 6c70fed..e59ea05 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -370,6 +370,17 @@ 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
    diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
    index 4eb5ce8..a3379a3 100644
    --- a/arch/x86/kernel/Makefile
    +++ b/arch/x86/kernel/Makefile
    @@ -77,6 +77,7 @@ 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
    diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
    new file mode 100644
    index 0000000..b999f5e
    --- /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);
    + }
    +}
    diff --git a/arch/x86/kernel/setup_32.c b/arch/x86/kernel/setup_32.c
    index 2b3e5d4..3ef92a2 100644
    --- a/arch/x86/kernel/setup_32.c
    +++ b/arch/x86/kernel/setup_32.c
    @@ -46,6 +46,7 @@
    #include <linux/pfn.h>
    #include <linux/pci.h>
    #include <linux/init_ohci1394_dma.h>
    +#include <linux/kvm_para.h>

    #include <video/edid.h>

    @@ -770,6 +771,10 @@ 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
    diff --git a/arch/x86/kernel/setup_64.c b/arch/x86/kernel/setup_64.c
    index f4f7ecf..26b676f 100644
    --- a/arch/x86/kernel/setup_64.c
    +++ b/arch/x86/kernel/setup_64.c
    @@ -41,6 +41,7 @@
    #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>
    @@ -349,6 +350,10 @@ 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;
    --
    1.5.4.5


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