riscv: mm: add _PAGE_LEAF macro

In riscv, a page table entry is leaf when any bit of read, write,
or execute bit is set. So add a macro:_PAGE_LEAF instead of
(_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC), which is frequently used
to determine if it is a leaf page. This make code easier to read,
without any functional change.
Signed-off-by: Nanyong Sun <sunnanyong@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/include/asm/pgtable-64.h

@@ -46,8 +46,7 @@ static inline int pud_bad(pud_t pud)
 #define pud_leaf	pud_leaf
 static inline int pud_leaf(pud_t pud)
 {
-	return pud_present(pud) &&
-	       (pud_val(pud) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC));
+	return pud_present(pud) && (pud_val(pud) & _PAGE_LEAF);
 }
 
 static inline void set_pud(pud_t *pudp, pud_t pud)

arch/riscv/include/asm/pgtable-bits.h

@@ -39,5 +39,10 @@
 #define _PAGE_CHG_MASK  (~(unsigned long)(_PAGE_PRESENT | _PAGE_READ |	\
 					  _PAGE_WRITE | _PAGE_EXEC |	\
 					  _PAGE_USER | _PAGE_GLOBAL))
+/*
+ * when all of R/W/X are zero, the PTE is a pointer to the next level
+ * of the page table; otherwise, it is a leaf PTE.
+ */
+#define _PAGE_LEAF (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC)
 
 #endif /* _ASM_RISCV_PGTABLE_BITS_H */

arch/riscv/include/asm/pgtable.h

@@ -190,8 +190,7 @@ static inline int pmd_bad(pmd_t pmd)
 #define pmd_leaf	pmd_leaf
 static inline int pmd_leaf(pmd_t pmd)
 {
-	return pmd_present(pmd) &&
-	       (pmd_val(pmd) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC));
+	return pmd_present(pmd) && (pmd_val(pmd) & _PAGE_LEAF);
 }
 
 static inline void set_pmd(pmd_t *pmdp, pmd_t pmd)
@@ -267,8 +266,7 @@ static inline int pte_exec(pte_t pte)
 
 static inline int pte_huge(pte_t pte)
 {
-	return pte_present(pte)
-		&& (pte_val(pte) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC));
+	return pte_present(pte) && (pte_val(pte) & _PAGE_LEAF);
 }
 
 static inline int pte_dirty(pte_t pte)