Commit e880c6ea authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Paolo Bonzini
Browse files

KVM: x86: hyper-v: Prevent using not-yet-updated TSC page by secondary CPUs 



When KVM_REQ_MASTERCLOCK_UPDATE request is issued (e.g. after migration)
we need to make sure no vCPU sees stale values in PV clock structures and
thus all vCPUs are kicked with KVM_REQ_CLOCK_UPDATE. Hyper-V TSC page
clocksource is global and kvm_guest_time_update() only updates in on vCPU0
but this is not entirely correct: nothing blocks some other vCPU from
entering the guest before we finish the update on CPU0 and it can read
stale values from the page.

Invalidate TSC page in kvm_gen_update_masterclock() to switch all vCPUs
to using MSR based clocksource (HV_X64_MSR_TIME_REF_COUNT).

Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210316143736.964151-3-vkuznets@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent d2547cf5

arch/x86/kvm/hyperv.c

+23 −0
Original line number Diff line number Diff line
@@ -1137,6 +1137,29 @@ void kvm_hv_setup_tsc_page(struct kvm *kvm, 
	mutex_unlock(&hv->hv_lock);

}



void kvm_hv_invalidate_tsc_page(struct kvm *kvm)

{

	struct kvm_hv *hv = to_kvm_hv(kvm);

	u64 gfn;



	if (!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE))

		return;



	mutex_lock(&hv->hv_lock);



	if (!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE))

		goto out_unlock;



	gfn = hv->hv_tsc_page >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;



	hv->tsc_ref.tsc_sequence = 0;

	kvm_write_guest(kvm, gfn_to_gpa(gfn),

			&hv->tsc_ref, sizeof(hv->tsc_ref.tsc_sequence));



out_unlock:

	mutex_unlock(&hv->hv_lock);

}



static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,

			     bool host)

{

arch/x86/kvm/hyperv.h

+1 −0
Original line number Diff line number Diff line
@@ -133,6 +133,7 @@ void kvm_hv_process_stimers(struct kvm_vcpu *vcpu); 


void kvm_hv_setup_tsc_page(struct kvm *kvm,

			   struct pvclock_vcpu_time_info *hv_clock);

void kvm_hv_invalidate_tsc_page(struct kvm *kvm);



void kvm_hv_init_vm(struct kvm *kvm);

void kvm_hv_destroy_vm(struct kvm *kvm);

arch/x86/kvm/x86.c

+2 −0
Original line number Diff line number Diff line
@@ -2551,6 +2551,8 @@ static void kvm_gen_update_masterclock(struct kvm *kvm) 
	struct kvm_vcpu *vcpu;

	struct kvm_arch *ka = &kvm->arch;



	kvm_hv_invalidate_tsc_page(kvm);



	spin_lock(&ka->pvclock_gtod_sync_lock);

	kvm_make_mclock_inprogress_request(kvm);

	/* no guest entries from this point */