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Commit 8b953440 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Radim Krčmář
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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: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
parent e5dbc4bf

arch/x86/kvm/x86.c

+13 −8
Original line number Diff line number Diff line
@@ -1724,18 +1724,23 @@ static void kvm_gen_update_masterclock(struct kvm *kvm) 


static u64 __get_kvmclock_ns(struct kvm *kvm)

{

	struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, 0);

	struct kvm_arch *ka = &kvm->arch;

	s64 ns;

	struct pvclock_vcpu_time_info hv_clock;



	if (vcpu->arch.hv_clock.flags & PVCLOCK_TSC_STABLE_BIT) {

		u64 tsc = kvm_read_l1_tsc(vcpu, rdtsc());

		ns = __pvclock_read_cycles(&vcpu->arch.hv_clock, tsc);

	} else {

		ns = ktime_get_boot_ns() + ka->kvmclock_offset;

	spin_lock(&ka->pvclock_gtod_sync_lock);

	if (!ka->use_master_clock) {

		spin_unlock(&ka->pvclock_gtod_sync_lock);

		return ktime_get_boot_ns() + ka->kvmclock_offset;

	}



	return ns;

	hv_clock.tsc_timestamp = ka->master_cycle_now;

	hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;

	spin_unlock(&ka->pvclock_gtod_sync_lock);



	kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,

			   &hv_clock.tsc_shift,

			   &hv_clock.tsc_to_system_mul);

	return __pvclock_read_cycles(&hv_clock, rdtsc());

}



u64 get_kvmclock_ns(struct kvm *kvm)