KVM: x86: Fix device passthrough when SME is active

When using device passthrough with SME active, the MMIO range that is
mapped for the device should not be mapped encrypted.  Add a check in
set_spte() to insure that a page is not mapped encrypted if that page
is a device MMIO page as indicated by kvm_is_mmio_pfn().

Cc: <stable@vger.kernel.org> # 4.14.x-
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -2770,9 +2770,11 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 	else
 		pte_access &= ~ACC_WRITE_MASK;
 
-	spte |= (u64)pfn << PAGE_SHIFT;
+	if (!kvm_is_mmio_pfn(pfn))
 		spte |= shadow_me_mask;
 
+	spte |= (u64)pfn << PAGE_SHIFT;
+
 	if (pte_access & ACC_WRITE_MASK) {
 
 		/*