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 int vcpu_mmio_write(struct kvm_vcpu *vcpu, gpa_t addr, int len,
			   const void *v)
{
	int handled = 0;
	int n;

	do {
		n = min(len, 8);
		if (!(vcpu->arch.apic &&
		      !kvm_iodevice_write(vcpu, &vcpu->arch.apic->dev, addr, n, v))
		    && kvm_io_bus_write(vcpu, KVM_MMIO_BUS, addr, n, v))
			break;
		handled += n;
		addr += n;
		len -= n;
		v += n;
	} while (len);

	return handled;
}

static int vcpu_mmio_write(struct kvm_vcpu *vcpu, gpa_t addr, int len,
			   const void *v)
{
	int handled = 0;
	int n;

	do {
		n = min(len, 8);
		if (!(vcpu->arch.apic &&
		      !kvm_iodevice_write(vcpu, &vcpu->arch.apic->dev, addr, n, v))
		    && kvm_io_bus_write(vcpu, KVM_MMIO_BUS, addr, n, v))
			break;
		handled += n;
		addr += n;
		len -= n;
		v += n;
	} while (len);

	return handled;
}
