From c807660407a695f390034e402edfe544a1d2e40c Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann Date: Wed, 4 Feb 2009 17:52:04 +0100 Subject: KVM: Fix kvmclock on !constant_tsc boxes kvmclock currently falls apart on machines without constant tsc. This patch fixes it. Changes: * keep tsc frequency in a per-cpu variable. * handle kvmclock update using a new request flag, thus checking whenever we need an update each time we enter guest context. * use a cpufreq notifier to track frequency changes and force kvmclock updates. * send ipis to kick cpu out of guest context if needed to make sure the guest doesn't see stale values. Signed-off-by: Gerd Hoffmann Signed-off-by: Avi Kivity --- arch/x86/kvm/x86.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 94 insertions(+), 9 deletions(-) (limited to 'arch/x86/kvm') diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 8f83590..05d7be8 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include @@ -617,6 +618,8 @@ static void kvm_set_time_scale(uint32_t tsc_khz, struct pvclock_vcpu_time_info * hv_clock->tsc_to_system_mul); } +static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz); + static void kvm_write_guest_time(struct kvm_vcpu *v) { struct timespec ts; @@ -627,9 +630,9 @@ static void kvm_write_guest_time(struct kvm_vcpu *v) if ((!vcpu->time_page)) return; - if (unlikely(vcpu->hv_clock_tsc_khz != tsc_khz)) { - kvm_set_time_scale(tsc_khz, &vcpu->hv_clock); - vcpu->hv_clock_tsc_khz = tsc_khz; + if (unlikely(vcpu->hv_clock_tsc_khz != __get_cpu_var(cpu_tsc_khz))) { + kvm_set_time_scale(__get_cpu_var(cpu_tsc_khz), &vcpu->hv_clock); + vcpu->hv_clock_tsc_khz = __get_cpu_var(cpu_tsc_khz); } /* Keep irq disabled to prevent changes to the clock */ @@ -660,6 +663,16 @@ static void kvm_write_guest_time(struct kvm_vcpu *v) mark_page_dirty(v->kvm, vcpu->time >> PAGE_SHIFT); } +static int kvm_request_guest_time_update(struct kvm_vcpu *v) +{ + struct kvm_vcpu_arch *vcpu = &v->arch; + + if (!vcpu->time_page) + return 0; + set_bit(KVM_REQ_KVMCLOCK_UPDATE, &v->requests); + return 1; +} + static bool msr_mtrr_valid(unsigned msr) { switch (msr) { @@ -790,7 +803,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data) vcpu->arch.time_page = NULL; } - kvm_write_guest_time(vcpu); + kvm_request_guest_time_update(vcpu); break; } default: @@ -1000,6 +1013,7 @@ int kvm_dev_ioctl_check_extension(long ext) case KVM_CAP_MMU_SHADOW_CACHE_CONTROL: case KVM_CAP_SET_TSS_ADDR: case KVM_CAP_EXT_CPUID: + case KVM_CAP_CLOCKSOURCE: case KVM_CAP_PIT: case KVM_CAP_NOP_IO_DELAY: case KVM_CAP_MP_STATE: @@ -1025,9 +1039,6 @@ int kvm_dev_ioctl_check_extension(long ext) case KVM_CAP_IOMMU: r = iommu_found(); break; - case KVM_CAP_CLOCKSOURCE: - r = boot_cpu_has(X86_FEATURE_CONSTANT_TSC); - break; default: r = 0; break; @@ -1098,7 +1109,7 @@ out: void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) { kvm_x86_ops->vcpu_load(vcpu, cpu); - kvm_write_guest_time(vcpu); + kvm_request_guest_time_update(vcpu); } void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) @@ -2642,9 +2653,72 @@ int kvm_emulate_pio_string(struct kvm_vcpu *vcpu, struct kvm_run *run, int in, } EXPORT_SYMBOL_GPL(kvm_emulate_pio_string); +static void bounce_off(void *info) +{ + /* nothing */ +} + +static unsigned int ref_freq; +static unsigned long tsc_khz_ref; + +static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long val, + void *data) +{ + struct cpufreq_freqs *freq = data; + struct kvm *kvm; + struct kvm_vcpu *vcpu; + int i, send_ipi = 0; + + if (!ref_freq) + ref_freq = freq->old; + + if (val == CPUFREQ_PRECHANGE && freq->old > freq->new) + return 0; + if (val == CPUFREQ_POSTCHANGE && freq->old < freq->new) + return 0; + per_cpu(cpu_tsc_khz, freq->cpu) = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new); + + spin_lock(&kvm_lock); + list_for_each_entry(kvm, &vm_list, vm_list) { + for (i = 0; i < KVM_MAX_VCPUS; ++i) { + vcpu = kvm->vcpus[i]; + if (!vcpu) + continue; + if (vcpu->cpu != freq->cpu) + continue; + if (!kvm_request_guest_time_update(vcpu)) + continue; + if (vcpu->cpu != smp_processor_id()) + send_ipi++; + } + } + spin_unlock(&kvm_lock); + + if (freq->old < freq->new && send_ipi) { + /* + * We upscale the frequency. Must make the guest + * doesn't see old kvmclock values while running with + * the new frequency, otherwise we risk the guest sees + * time go backwards. + * + * In case we update the frequency for another cpu + * (which might be in guest context) send an interrupt + * to kick the cpu out of guest context. Next time + * guest context is entered kvmclock will be updated, + * so the guest will not see stale values. + */ + smp_call_function_single(freq->cpu, bounce_off, NULL, 1); + } + return 0; +} + +static struct notifier_block kvmclock_cpufreq_notifier_block = { + .notifier_call = kvmclock_cpufreq_notifier +}; + int kvm_arch_init(void *opaque) { - int r; + int r, cpu; struct kvm_x86_ops *ops = (struct kvm_x86_ops *)opaque; if (kvm_x86_ops) { @@ -2675,6 +2749,15 @@ int kvm_arch_init(void *opaque) kvm_mmu_set_base_ptes(PT_PRESENT_MASK); kvm_mmu_set_mask_ptes(PT_USER_MASK, PT_ACCESSED_MASK, PT_DIRTY_MASK, PT64_NX_MASK, 0, 0); + + for_each_possible_cpu(cpu) + per_cpu(cpu_tsc_khz, cpu) = tsc_khz; + if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) { + tsc_khz_ref = tsc_khz; + cpufreq_register_notifier(&kvmclock_cpufreq_notifier_block, + CPUFREQ_TRANSITION_NOTIFIER); + } + return 0; out: @@ -3010,6 +3093,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) if (vcpu->requests) { if (test_and_clear_bit(KVM_REQ_MIGRATE_TIMER, &vcpu->requests)) __kvm_migrate_timers(vcpu); + if (test_and_clear_bit(KVM_REQ_KVMCLOCK_UPDATE, &vcpu->requests)) + kvm_write_guest_time(vcpu); if (test_and_clear_bit(KVM_REQ_MMU_SYNC, &vcpu->requests)) kvm_mmu_sync_roots(vcpu); if (test_and_clear_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests)) -- cgit v1.1