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KVM: x86: do not go through vcpu in __get_kvmclock_ns
Going through the first VCPU is wrong if you follow a KVM_SET_CLOCK with a KVM_GET_CLOCK immediately after, without letting the VCPU run and call kvm_guest_time_update. To fix this, compute the kvmclock value ourselves, using the master clock (tsc, nsec) pair as the base and the host CPU frequency as the scale. Reported-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
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1 changed files with 13 additions and 8 deletions
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@ -1724,18 +1724,23 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
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static u64 __get_kvmclock_ns(struct kvm *kvm)
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{
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struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, 0);
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struct kvm_arch *ka = &kvm->arch;
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s64 ns;
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struct pvclock_vcpu_time_info hv_clock;
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if (vcpu->arch.hv_clock.flags & PVCLOCK_TSC_STABLE_BIT) {
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u64 tsc = kvm_read_l1_tsc(vcpu, rdtsc());
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ns = __pvclock_read_cycles(&vcpu->arch.hv_clock, tsc);
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} else {
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ns = ktime_get_boot_ns() + ka->kvmclock_offset;
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spin_lock(&ka->pvclock_gtod_sync_lock);
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if (!ka->use_master_clock) {
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spin_unlock(&ka->pvclock_gtod_sync_lock);
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return ktime_get_boot_ns() + ka->kvmclock_offset;
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}
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return ns;
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hv_clock.tsc_timestamp = ka->master_cycle_now;
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hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
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spin_unlock(&ka->pvclock_gtod_sync_lock);
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kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
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&hv_clock.tsc_shift,
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&hv_clock.tsc_to_system_mul);
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return __pvclock_read_cycles(&hv_clock, rdtsc());
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}
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u64 get_kvmclock_ns(struct kvm *kvm)
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