kvm: Obey read-only mappings in iommu

We've been ignoring read-only mappings and programming everything
into the iommu as read-write.  Fix this to only include the write
access flag when read-only is not set.
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

virt/kvm/iommu.c

@@ -76,7 +76,9 @@ int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
 	gfn     = slot->base_gfn;
 	end_gfn = gfn + slot->npages;
 
-	flags = IOMMU_READ | IOMMU_WRITE;
+	flags = IOMMU_READ;
+	if (!(slot->flags & KVM_MEM_READONLY))
+		flags |= IOMMU_WRITE;
 	if (kvm->arch.iommu_flags & KVM_IOMMU_CACHE_COHERENCY)
 		flags |= IOMMU_CACHE;