powerpc/64: Add VIRTUAL_BUG_ON checks for __va and __pa addresses

Ensure __va is given a physical address below PAGE_OFFSET, and __pa is
given a virtual address above PAGE_OFFSET.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190724084638.24982-4-npiggin@gmail.com

arch/powerpc/include/asm/page.h

@@ -215,9 +215,19 @@ static inline bool pfn_valid(unsigned long pfn)
 /*
  * gcc miscompiles (unsigned long)(&static_var) - PAGE_OFFSET
  * with -mcmodel=medium, so we use & and | instead of - and + on 64-bit.
+ * This also results in better code generation.
  */
-#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) | PAGE_OFFSET))
-#define __pa(x) ((unsigned long)(x) & 0x0fffffffffffffffUL)
+#define __va(x)								\
+({									\
+	VIRTUAL_BUG_ON((unsigned long)(x) >= PAGE_OFFSET);		\
+	(void *)(unsigned long)((phys_addr_t)(x) | PAGE_OFFSET);	\
+})
+
+#define __pa(x)								\
+({									\
+	VIRTUAL_BUG_ON((unsigned long)(x) < PAGE_OFFSET);		\
+	(unsigned long)(x) & 0x0fffffffffffffffUL;			\
+})
 
 #else /* 32-bit, non book E */
 #define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) + PAGE_OFFSET - MEMORY_START))