[PATCH 2/3] powerpc: mm: add p{te,md,ud}_user_accessible_page helpers

[Rohan McLure <rmclure@linux.ibm.com>]

Add the following helpers for detecting whether a page table entry
is a leaf and is accessible to user space.

 * pte_user_accessible_page
 * pmd_user_accessible_page
 * pud_user_accessible_page

The heavy lifting is done by pte_user, which checks user accessibility
on a per-mmu level, provided prior to this commit.

On 32-bit systems, provide stub implementations for these methods, with
BUG(), as debug features such as page table checks will emit functions
that call p{md,ud}_user_accessible_page but must not be used.

Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
---
 arch/powerpc/include/asm/pgtable.h | 35 ++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index 522145b16a07..8c1f5feb9360 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h
@@ -170,6 +170,41 @@ static inline int pud_pfn(pud_t pud)
 	return 0;
 }
 
+static inline bool pte_user_accessible_page(pte_t pte)
+{
+	return (pte_val(pte) & _PAGE_PRESENT) && pte_user(pte);
+}
+
+#ifdef CONFIG_PPC64
+
+static inline bool pmd_user_accessible_page(pmd_t pmd)
+{
+	return pmd_is_leaf(pmd) && pmd_present(pmd)
+				&& pte_user(pmd_pte(pmd));
+}
+
+static inline bool pud_user_accessible_page(pud_t pud)
+{
+	return pud_is_leaf(pud) && pud_present(pud)
+				&& pte_user(pud_pte(pud));
+}
+
+#else
+
+static inline bool pmd_user_accessible_page(pmd_t pmd)
+{
+	BUG();
+	return false;
+}
+
+static inline bool pud_user_accessible_page(pud_t pud)
+{
+	BUG();
+	return false;
+}
+
+#endif /* CONFIG_PPC64 */
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_POWERPC_PGTABLE_H */
-- 
2.34.1