powerpc: Fail remap_4k_pfn() if PFN doesn't fit inside PTE

remap_4k_pfn() silently truncates upper bits of input 4K PFN
if it cannot be contained in PTE. This leads invalid memory mapping and could
result in a system crash when the memory is accessed. This patch fails
remap_4k_pfn() and returns -EINVAL if the input 4K PFN cannot be contained in
PTE.

V3 : Added parentheses to protect 'pfn' and entire macro as suggested by Brian.
V2 : Rewritten to avoid helper function as suggested by Stephen Rothwell.
Signed-off-by: Madhusudanan Kandasamy <kmadhu@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/pte-hash64-64k.h

@@ -75,7 +75,8 @@
 	(((pte) & _PAGE_COMBO)? MMU_PAGE_4K: MMU_PAGE_64K)
 
 #define remap_4k_pfn(vma, addr, pfn, prot)				\
-	remap_pfn_range((vma), (addr), (pfn), PAGE_SIZE,		\
-			__pgprot(pgprot_val((prot)) | _PAGE_4K_PFN))
+	(WARN_ON(((pfn) >= (1UL << (64 - PTE_RPN_SHIFT)))) ? -EINVAL :	\
+		remap_pfn_range((vma), (addr), (pfn), PAGE_SIZE,	\
+			__pgprot(pgprot_val((prot)) | _PAGE_4K_PFN)))
 
 #endif	/* __ASSEMBLY__ */