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Commit 78db6a50 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: x86: rewrite handling of scaled TSC for kvmclock 



This is the same as before:

    kvm_scale_tsc(tgt_tsc_khz)
        = tgt_tsc_khz * ratio
        = tgt_tsc_khz * user_tsc_khz / tsc_khz   (see set_tsc_khz)
        = user_tsc_khz                           (see kvm_guest_time_update)
        = vcpu->arch.virtual_tsc_khz             (see kvm_set_tsc_khz)

However, computing it through kvm_scale_tsc will make it possible
to include the NTP correction in tgt_tsc_khz.

Reviewed-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 4941b8cb

arch/x86/kvm/x86.c

+8 −7
Original line number Diff line number Diff line
@@ -1713,7 +1713,7 @@ static void kvm_gen_update_masterclock(struct kvm *kvm) 


static int kvm_guest_time_update(struct kvm_vcpu *v)

{

	unsigned long flags, this_tsc_khz, tgt_tsc_khz;

	unsigned long flags, tgt_tsc_khz;

	struct kvm_vcpu_arch *vcpu = &v->arch;

	struct kvm_arch *ka = &v->kvm->arch;

	s64 kernel_ns;
@@ -1739,8 +1739,8 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) 


	/* Keep irq disabled to prevent changes to the clock */

	local_irq_save(flags);

	this_tsc_khz = __this_cpu_read(cpu_tsc_khz);

	if (unlikely(this_tsc_khz == 0)) {

	tgt_tsc_khz = __this_cpu_read(cpu_tsc_khz);

	if (unlikely(tgt_tsc_khz == 0)) {

		local_irq_restore(flags);

		kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);

		return 1;
@@ -1775,13 +1775,14 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) 
	if (!vcpu->pv_time_enabled)

		return 0;



	if (unlikely(vcpu->hw_tsc_khz != this_tsc_khz)) {

		tgt_tsc_khz = kvm_has_tsc_control ?

			vcpu->virtual_tsc_khz : this_tsc_khz;

	if (kvm_has_tsc_control)

		tgt_tsc_khz = kvm_scale_tsc(v, tgt_tsc_khz);



	if (unlikely(vcpu->hw_tsc_khz != tgt_tsc_khz)) {

		kvm_get_time_scale(NSEC_PER_SEC / 1000, tgt_tsc_khz,

				   &vcpu->hv_clock.tsc_shift,

				   &vcpu->hv_clock.tsc_to_system_mul);

		vcpu->hw_tsc_khz = this_tsc_khz;

		vcpu->hw_tsc_khz = tgt_tsc_khz;

	}



	/* With all the info we got, fill in the values */