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KVM: Fix kvmclock on !constant_tsc boxes

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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>
This commit is contained in:
Gerd Hoffmann 2009-02-04 17:52:04 +01:00 committed by Avi Kivity
parent 49cd7d2238
commit c807660407
2 changed files with 95 additions and 9 deletions
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103
arch/x86/kvm/x86.c
View File

@ -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))

1
include/linux/kvm_host.h
View File

@ -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