+/*
+ * hv_set_mem_host_visibility - Set host visibility for specified memory.
+ */

I don't think this comment really clarifies anything over the function
name.  What is 'host visibility'

+int hv_set_mem_host_visibility(void *kbuffer, u32 size, u32 visibility)

Should size be a size_t?
Should visibility be an enum of some kind?

+int hv_mark_gpa_visibility(u16 count, const u64 pfn[], u32 visibility)

Not sure what this does either.

+	local_irq_save(flags);
+	input_pcpu = (struct hv_input_modify_sparse_gpa_page_host_visibility **)

Is there a chance we could find a shorter but still descriptive
name for this variable?  Why do we need the cast?

+#define VMBUS_PAGE_VISIBLE_READ_ONLY HV_MAP_GPA_READABLE
+#define VMBUS_PAGE_VISIBLE_READ_WRITE (HV_MAP_GPA_READABLE|HV_MAP_GPA_WRITABLE)

pointlessly overlong line.