powerpc/mm/book3s64/hash/4k: Add pmd_same callback for 4K page size

With commit 0d940a9 ("mm/pgtable: allow pte_offset_map[_lock]() to
fail") the kernel is now using pmd_same to compare pmd values that are
pointing to a level 4 page table page. Move the functions out of #ifdef
CONFIG_TRANSPARENT_HUGEPAGE and add a variant that can work with both 4K
and 64K page size.

kernel BUG at arch/powerpc/include/asm/book3s/64/hash-4k.h:141!
Oops: Exception in kernel mode, sig: 5 [#1]
LE PAGE_SIZE=4K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
.....
NIP [c00000000048aee0] __pte_offset_map_lock+0xf0/0x164
LR [c00000000048ae78] __pte_offset_map_lock+0x88/0x164
Call Trace:
 0xc0003f000009a340 (unreliable)
 __handle_mm_fault+0x1340/0x1980
 handle_mm_fault+0xbc/0x380
 __get_user_pages+0x320/0x550
 get_user_pages_remote+0x13c/0x520
 get_arg_page+0x80/0x1d0
 copy_string_kernel+0xc8/0x250
 kernel_execve+0x11c/0x270
 run_init_process+0xe4/0x10c
 kernel_init+0xbc/0x1a0
 ret_from_kernel_user_thread+0x14/0x1c

Reported-by: Michael Ellerman <[email protected]>
Signed-off-by: "Aneesh Kumar K.V" <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://msgid.link/[email protected]

Author: kvaneesh

arch/powerpc/include/asm/book3s/64/hash-4k.h

@@ -136,12 +136,6 @@ static inline int hash__pmd_trans_huge(pmd_t pmd)
 	return 0;
 }
 
-static inline int hash__pmd_same(pmd_t pmd_a, pmd_t pmd_b)
-{
-	BUG();
-	return 0;
-}
-
 static inline pmd_t hash__pmd_mkhuge(pmd_t pmd)
 {
 	BUG();

arch/powerpc/include/asm/book3s/64/hash-64k.h

@@ -263,11 +263,6 @@ static inline int hash__pmd_trans_huge(pmd_t pmd)
 		  (_PAGE_PTE | H_PAGE_THP_HUGE));
 }
 
-static inline int hash__pmd_same(pmd_t pmd_a, pmd_t pmd_b)
-{
-	return (((pmd_raw(pmd_a) ^ pmd_raw(pmd_b)) & ~cpu_to_be64(_PAGE_HPTEFLAGS)) == 0);
-}
-
 static inline pmd_t hash__pmd_mkhuge(pmd_t pmd)
 {
 	return __pmd(pmd_val(pmd) | (_PAGE_PTE | H_PAGE_THP_HUGE));

arch/powerpc/include/asm/book3s/64/hash.h

@@ -132,6 +132,11 @@ static inline int get_region_id(unsigned long ea)
 	return region_id;
 }
 
+static inline int hash__pmd_same(pmd_t pmd_a, pmd_t pmd_b)
+{
+	return (((pmd_raw(pmd_a) ^ pmd_raw(pmd_b)) & ~cpu_to_be64(_PAGE_HPTEFLAGS)) == 0);
+}
+
 #define	hash__pmd_bad(pmd)		(pmd_val(pmd) & H_PMD_BAD_BITS)
 #define	hash__pud_bad(pud)		(pud_val(pud) & H_PUD_BAD_BITS)
 static inline int hash__p4d_bad(p4d_t p4d)