ARM: mm: introduce L_PTE_VALID for page table entries

For long-descriptor translation table formats, the ARMv7 architecture
defines the last two bits of the second- and third-level descriptors to
be:

	x0b	- Invalid
	01b	- Block (second-level), Reserved (third-level)
	11b	- Table (second-level), Page (third-level)

This allows us to define L_PTE_PRESENT as (3 << 0) and use this value to
create ptes directly. However, when determining whether a given pte
value is present in the low-level page table accessors, we only need to
check the least significant bit of the descriptor, allowing us to write
faulting, present entries which are required for PROT_NONE mappings.

This patch introduces L_PTE_VALID, which can be used to test whether a
pte should fault, and updates the low-level page table accessors
accordingly.

Signed-off-by: Will Deacon <will.deacon@arm.com>

3 files changed, 4 insertions, 4 deletions

diff --git a/arch/arm/include/asm/pgtable-2level.h b/arch/arm/include/asm/pgtable-2level.h
index 2317a71c8f8e..c44a1ecfc28a 100644
--- a/arch/arm/include/asm/pgtable-2level.h
+++ b/arch/arm/include/asm/pgtable-2level.h
@@ -115,6 +115,7 @@
  * The PTE table pointer refers to the hardware entries; the "Linux"
  * entries are stored 1024 bytes below.
  */
+#define L_PTE_VALID             (_AT(pteval_t, 1) << 0)         /* Valid */
 #define L_PTE_PRESENT           (_AT(pteval_t, 1) << 0)
 #define L_PTE_YOUNG             (_AT(pteval_t, 1) << 1)
 #define L_PTE_FILE              (_AT(pteval_t, 1) << 2) /* only when !PRESENT */
diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
index b24903549d1c..e32311a9abca 100644
--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h
@@ -67,7 +67,8 @@
  * These bits overlap with the hardware bits but the naming is preserved for
  * consistency with the classic page table format.
  */
-#define L_PTE_PRESENT           (_AT(pteval_t, 3) << 0)         /* Valid */
+#define L_PTE_VALID             (_AT(pteval_t, 1) << 0)         /* Valid */
+#define L_PTE_PRESENT           (_AT(pteval_t, 3) << 0)         /* Present */
 #define L_PTE_FILE              (_AT(pteval_t, 1) << 2)         /* only when !PRESENT */
 #define L_PTE_USER              (_AT(pteval_t, 1) << 6)         /* AP[1] */
 #define L_PTE_RDONLY            (_AT(pteval_t, 1) << 7)         /* AP[2] */
diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index 08c12312a1f9..ccf34b6e9903 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -203,9 +203,7 @@ static inline pte_t *pmd_page_vaddr(pmd_t pmd)
 #define pte_exec(pte)           (!(pte_val(pte) & L_PTE_XN))
 #define pte_special(pte)        (0)
 
-#define pte_present_user(pte) \
-        ((pte_val(pte) & (L_PTE_PRESENT | L_PTE_USER)) == \
-         (L_PTE_PRESENT | L_PTE_USER))
+#define pte_present_user(pte)  (pte_present(pte) && (pte_val(pte) & L_PTE_USER))
 
 #if __LINUX_ARM_ARCH__ < 6
 static inline void __sync_icache_dcache(pte_t pteval)