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    Subject[PATCH 3/5] Try using new kvm clock msrs
    Date
    We now added a new set of clock-related msrs in replacement of the old
    ones. In theory, we could just try to use them and get a return value
    indicating they do not exist, due to our use of kvm_write_msr_save.

    However, kvm clock registration happens very early, and if we ever
    try to write to a non-existant MSR, we raise a lethal #GP, since our
    idt handlers are not in place yet.

    So this patch tests for a cpuid feature exported by the host to
    decide which set of msrs are supported.

    Signed-off-by: Glauber Costa <glommer@redhat.com>
    ---
    arch/x86/include/asm/kvm_para.h | 4 ++
    arch/x86/kernel/kvmclock.c | 68 +++++++++++++++++++++++++++------------
    2 files changed, 51 insertions(+), 21 deletions(-)

    diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
    index 0cffb96..a32710a 100644
    --- a/arch/x86/include/asm/kvm_para.h
    +++ b/arch/x86/include/asm/kvm_para.h
    @@ -16,6 +16,10 @@
    #define KVM_FEATURE_CLOCKSOURCE 0
    #define KVM_FEATURE_NOP_IO_DELAY 1
    #define KVM_FEATURE_MMU_OP 2
    +/* We could just try to use new msr values, but they are queried very early,
    + * kernel does not have idt handlers yet, and failures are fatal */
    +#define KVM_FEATURE_CLOCKSOURCE2 3
    +

    #define MSR_KVM_WALL_CLOCK_OLD 0x11
    #define MSR_KVM_SYSTEM_TIME_OLD 0x12
    diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
    index feaeb0d..6d814ce 100644
    --- a/arch/x86/kernel/kvmclock.c
    +++ b/arch/x86/kernel/kvmclock.c
    @@ -29,6 +29,7 @@
    #define KVM_SCALE 22

    static int kvmclock = 1;
    +static int kvm_use_new_msrs = 0;

    static int parse_no_kvmclock(char *arg)
    {
    @@ -41,6 +42,18 @@ early_param("no-kvmclock", parse_no_kvmclock);
    static DEFINE_PER_CPU_SHARED_ALIGNED(struct pvclock_vcpu_time_info, hv_clock);
    static struct pvclock_wall_clock wall_clock;

    +static int kvm_system_time_write_value(int low, int high)
    +{
    + if (kvm_use_new_msrs)
    + return native_write_msr_safe(MSR_KVM_SYSTEM_TIME_OLD, low, high);
    + else
    + return native_write_msr_safe(MSR_KVM_SYSTEM_TIME, low, high);
    +}
    +
    +static void kvm_turnoff_clock(void)
    +{
    + kvm_system_time_write_value(0, 0);
    +}
    /*
    * 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
    @@ -54,7 +67,11 @@ static unsigned long kvm_get_wallclock(void)

    low = (int)__pa_symbol(&wall_clock);
    high = ((u64)__pa_symbol(&wall_clock) >> 32);
    - native_write_msr(MSR_KVM_WALL_CLOCK, low, high);
    +
    + if (kvm_use_new_msrs)
    + native_write_msr_safe(MSR_KVM_WALL_CLOCK, low, high);
    + else
    + native_write_msr(MSR_KVM_WALL_CLOCK_OLD, low, high);

    vcpu_time = &get_cpu_var(hv_clock);
    pvclock_read_wallclock(&wall_clock, vcpu_time, &ts);
    @@ -130,7 +147,8 @@ static int kvm_register_clock(char *txt)
    high = ((u64)__pa(&per_cpu(hv_clock, cpu)) >> 32);
    printk(KERN_INFO "kvm-clock: cpu %d, msr %x:%x, %s\n",
    cpu, high, low, txt);
    - return native_write_msr_safe(MSR_KVM_SYSTEM_TIME, low, high);
    +
    + return kvm_system_time_write_value(low, high);
    }

    #ifdef CONFIG_X86_LOCAL_APIC
    @@ -165,14 +183,14 @@ static void __init kvm_smp_prepare_boot_cpu(void)
    #ifdef CONFIG_KEXEC
    static void kvm_crash_shutdown(struct pt_regs *regs)
    {
    - native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0);
    + kvm_turnoff_clock();
    native_machine_crash_shutdown(regs);
    }
    #endif

    static void kvm_shutdown(void)
    {
    - native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0);
    + kvm_turnoff_clock();
    native_machine_shutdown();
    }

    @@ -181,27 +199,35 @@ void __init kvmclock_init(void)
    if (!kvm_para_available())
    return;

    - if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
    - if (kvm_register_clock("boot clock"))
    - return;
    - pv_time_ops.sched_clock = kvm_clock_read;
    - x86_platform.calibrate_tsc = kvm_get_tsc_khz;
    - x86_platform.get_wallclock = kvm_get_wallclock;
    - x86_platform.set_wallclock = kvm_set_wallclock;
    + if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2))
    + kvm_use_new_msrs = 1;
    + else if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE))
    + kvm_use_new_msrs = 0;
    + else
    + return;
    +
    + printk(KERN_INFO "kvm-clock: %ssing clocksource new msrs",
    + kvm_use_new_msrs ? "U": "Not u");
    +
    + if (kvm_register_clock("boot clock"))
    + return;
    + pv_time_ops.sched_clock = kvm_clock_read;
    + x86_platform.calibrate_tsc = kvm_get_tsc_khz;
    + x86_platform.get_wallclock = kvm_get_wallclock;
    + x86_platform.set_wallclock = kvm_set_wallclock;
    #ifdef CONFIG_X86_LOCAL_APIC
    - x86_cpuinit.setup_percpu_clockev =
    - kvm_setup_secondary_clock;
    + x86_cpuinit.setup_percpu_clockev =
    + kvm_setup_secondary_clock;
    #endif
    #ifdef CONFIG_SMP
    - smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
    + smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
    #endif
    - machine_ops.shutdown = kvm_shutdown;
    + machine_ops.shutdown = kvm_shutdown;
    #ifdef CONFIG_KEXEC
    - machine_ops.crash_shutdown = kvm_crash_shutdown;
    + machine_ops.crash_shutdown = kvm_crash_shutdown;
    #endif
    - kvm_get_preset_lpj();
    - clocksource_register(&kvm_clock);
    - pv_info.paravirt_enabled = 1;
    - pv_info.name = "KVM";
    - }
    + kvm_get_preset_lpj();
    + clocksource_register(&kvm_clock);
    + pv_info.paravirt_enabled = 1;
    + pv_info.name = "KVM";
    }
    --
    1.6.2.2


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