ARC: Fix PAE40 boot failures due to PTE truncation

So a benign looking cleanup which macro'ized PAGE_SHIFT shifts turned
out to be bad (since it was done non-sensically across the board).

It caused boot failures with PAE40 as forced cast to (unsigned long)
from newly introduced virt_to_pfn() was causing truncatiion of the
(long long) pte/paddr values.

It is OK to use this in accessors dealing with kernel virtual address,
pointers etc, but not for PTE values themelves.

Fixes: cJ2ff5cf2735c ("ARC: mm: Use virt_to_pfn() for addr >> PAGE_SHIFT pattern)
Signed-off-by: Vineet Gupta <[e-mail]>

arch/arc/include/asm/page.h

···
 
 typedef pte_t * pgtable_t;
 
+/*
+ * Use virt_to_pfn with caution:
+ * If used in pte or paddr related macros, it could cause truncation
+ * in PAE40 builds
+ * As a rule of thumb, only use it in helpers starting with virt_
+ * You have been warned !
+ */
 #define virt_to_pfn(kaddr)	(__pa(kaddr) >> PAGE_SHIFT)
 
 #define ARCH_PFN_OFFSET		virt_to_pfn(CONFIG_LINUX_LINK_BASE)
···
  * virt here means link-address/program-address as embedded in object code.
  * And for ARC, link-addr = physical address
  */
-#define __pa(vaddr)  ((unsigned long)vaddr)
+#define __pa(vaddr)  ((unsigned long)(vaddr))
 #define __va(paddr)  ((void *)((unsigned long)(paddr)))
 
 #define virt_to_page(kaddr)	\

arch/arc/include/asm/pgtable.h

···
 #define pmd_present(x)			(pmd_val(x))
 #define pmd_clear(xp)			do { pmd_val(*(xp)) = 0; } while (0)
 
-#define pte_page(pte)	\
-	(mem_map + virt_to_pfn(pte_val(pte) - CONFIG_LINUX_LINK_BASE))
-
+#define pte_page(pte)		pfn_to_page(pte_pfn(pte))
 #define mk_pte(page, prot)	pfn_pte(page_to_pfn(page), prot)
-#define pte_pfn(pte)		virt_to_pfn(pte_val(pte))
-#define pfn_pte(pfn, prot)	(__pte(((pte_t)(pfn) << PAGE_SHIFT) | \
-				 pgprot_val(prot)))
-#define __pte_index(addr)	(virt_to_pfn(addr) & (PTRS_PER_PTE - 1))
+#define pfn_pte(pfn, prot)	(__pte(((pte_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
+
+/* Don't use virt_to_pfn for macros below: could cause truncations for PAE40*/
+#define pte_pfn(pte)		(pte_val(pte) >> PAGE_SHIFT)
+#define __pte_index(addr)	(((addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1))
 
 /*
  * pte_offset gets a @ptr to PMD entry (PGD in our 2-tier paging system)