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 <kraxel@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8f83590..05d7be8 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -36,6 +36,7 @@
 #include <linux/highmem.h>
 #include <linux/iommu.h>
 #include <linux/intel-iommu.h>
+#include <linux/cpufreq.h>
 
 #include <asm/uaccess.h>
 #include <asm/msr.h>
@@ -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))

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 339eda3..18b4df8 100644 (file)
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -37,6 +37,7 @@
 #define KVM_REQ_PENDING_TIMER      5
 #define KVM_REQ_UNHALT             6
 #define KVM_REQ_MMU_SYNC           7
+#define KVM_REQ_KVMCLOCK_UPDATE    8
 
 #define KVM_USERSPACE_IRQ_SOURCE_ID    0