KVM: x86: pvclock: Handle first-time write to pvclock-page contains random junk

When guest passes KVM it's pvclock-page GPA via WRMSR to
MSR_KVM_SYSTEM_TIME / MSR_KVM_SYSTEM_TIME_NEW, KVM don't initialize
pvclock-page to some start-values. It just requests a clock-update which
will happen before entering to guest.

The clock-update logic will call kvm_setup_pvclock_page() to update the
pvclock-page with info. However, kvm_setup_pvclock_page() *wrongly*
assumes that the version-field is initialized to an even number. This is
wrong because at first-time write, field could be any-value.

Fix simply makes sure that if first-time version-field is odd, increment
it once more to make it even and only then start standard logic.
This follows same logic as done in other pvclock shared-pages (See
kvm_write_wall_clock() and record_steal_time()).
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/x86.c

@@ -1830,6 +1830,9 @@ static void kvm_setup_pvclock_page(struct kvm_vcpu *v)
 	 */
 	BUILD_BUG_ON(offsetof(struct pvclock_vcpu_time_info, version) != 0);
 
+	if (guest_hv_clock.version & 1)
+		++guest_hv_clock.version;  /* first time write, random junk */
+
 	vcpu->hv_clock.version = guest_hv_clock.version + 1;
 	kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
 				&vcpu->hv_clock,