UPSTREAM: asm-generic: add an optional pfn_valid check to page_to_phys

page_to_pfn is usually implemented by pointer arithmetics on the memory
map, which means that bogus input can lead to even more bogus output.

Powerpc had a pfn_valid check on the intermediate pfn in the page_to_phys
implementation when CONFIG_DEBUG_VIRTUAL is defined, which seems
generally useful, so add that to the generic version.

Bug: 399192075

Change-Id: I078e75dbecaac9f70306ed8472ab1d68c97ad2f5
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
(cherry picked from commit 3e25d5a49f99b75be2c6cfb165e4f77dc6d739a2)
Signed-off-by: Sandeep Dhavale <dhavale@google.com>

include/asm-generic/memory_model.h

@@ -64,7 +64,17 @@ static inline int pfn_valid(unsigned long pfn)
 #define page_to_pfn __page_to_pfn
 #define pfn_to_page __pfn_to_page
 
+#ifdef CONFIG_DEBUG_VIRTUAL
+#define page_to_phys(page)						\
+({									\
+	unsigned long __pfn = page_to_pfn(page);			\
+									\
+	WARN_ON_ONCE(!pfn_valid(__pfn));				\
+	PFN_PHYS(__pfn);						\
+})
+#else
 #define page_to_phys(page)	PFN_PHYS(page_to_pfn(page))
+#endif /* CONFIG_DEBUG_VIRTUAL */
 #define phys_to_page(phys)	pfn_to_page(PHYS_PFN(phys))
 
 #endif /* __ASSEMBLY__ */