KVM: x86: Reload pit counters for all channels when restoring state

Currently if userspace restores the pit counters with a count of 0
on channels 1 or 2 and the guest attempts to read the count on those
channels, then KVM will perform a mod of 0 and crash.  This will ensure
that 0 values are converted to 65536 as per the spec.

This is CVE-2015-7513.

Signed-off-by: Andy Honig <ahonig@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
{
	if (!list_empty_careful(&vcpu->async_pf.done))
		return true;

	if (kvm_apic_has_events(vcpu))
		return true;

	if (vcpu->arch.pv.pv_unhalted)
		return true;

	if (atomic_read(&vcpu->arch.nmi_queued))
		return true;

	if (test_bit(KVM_REQ_SMI, &vcpu->requests))
		return true;

	if (kvm_arch_interrupt_allowed(vcpu) &&
	    kvm_cpu_has_interrupt(vcpu))
		return true;

	return false;
}

static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
{
	if (!list_empty_careful(&vcpu->async_pf.done))
		return true;

	if (kvm_apic_has_events(vcpu))
		return true;

	if (vcpu->arch.pv.pv_unhalted)
		return true;

	if (atomic_read(&vcpu->arch.nmi_queued))
		return true;

	if (test_bit(KVM_REQ_SMI, &vcpu->requests))
		return true;

	if (kvm_arch_interrupt_allowed(vcpu) &&
	    kvm_cpu_has_interrupt(vcpu))
		return true;

	return false;
}
