[PATCH v2 19/19] ARC: mm: introduce _PAGE_TABLE to explicitly link pgd,pud,pmd entries

[Vineet Gupta <vgupta@kernel.org>]

ARCv3 hardware walker expects Table Descriptors to have b'11 in LSB bits
to continue moving to next level.

This commits adds that (to ARCv2 code) and ensures that it works in
software walked regime.

The pte entries stil need tagging, but that is not possible in ARCv2
since the LSB 2 bits are currently used.

Signed-off-by: Vineet Gupta <vgupta@kernel.org>
---
 arch/arc/include/asm/pgalloc.h            | 8 ++++----
 arch/arc/include/asm/pgtable-bits-arcv2.h | 2 ++
 arch/arc/include/asm/pgtable-levels.h     | 6 +++---
 arch/arc/mm/tlbex.S                       | 4 +++-
 4 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/arch/arc/include/asm/pgalloc.h b/arch/arc/include/asm/pgalloc.h
index 096b8ef58edb..a8c01eceba1b 100644
--- a/arch/arc/include/asm/pgalloc.h
+++ b/arch/arc/include/asm/pgalloc.h
@@ -43,12 +43,12 @@ pmd_populate_kernel(struct mm_struct *mm, pmd_t *pmd, pte_t *pte)
 	 *
 	 * The cast itself is needed given simplistic definition of set_pmd()
 	 */
-	set_pmd(pmd, __pmd((unsigned long)pte));
+	set_pmd(pmd, __pmd((unsigned long)pte | _PAGE_TABLE));
 }
 
 static inline void pmd_populate(struct mm_struct *mm, pmd_t *pmd, pgtable_t pte_page)
 {
-	set_pmd(pmd, __pmd((unsigned long)page_address(pte_page)));
+	set_pmd(pmd, __pmd((unsigned long)page_address(pte_page) | _PAGE_TABLE));
 }
 
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
@@ -74,7 +74,7 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 
 static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
 {
-	set_p4d(p4dp, __p4d((unsigned long)pudp));
+	set_p4d(p4dp, __p4d((unsigned long)pudp | _PAGE_TABLE));
 }
 
 #define __pud_free_tlb(tlb, pmd, addr)  pud_free((tlb)->mm, pmd)
@@ -85,7 +85,7 @@ static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
 
 static inline void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmdp)
 {
-	set_pud(pudp, __pud((unsigned long)pmdp));
+	set_pud(pudp, __pud((unsigned long)pmdp | _PAGE_TABLE));
 }
 
 #define __pmd_free_tlb(tlb, pmd, addr)  pmd_free((tlb)->mm, pmd)
diff --git a/arch/arc/include/asm/pgtable-bits-arcv2.h b/arch/arc/include/asm/pgtable-bits-arcv2.h
index 183d23bc1e00..54aba0d3ae34 100644
--- a/arch/arc/include/asm/pgtable-bits-arcv2.h
+++ b/arch/arc/include/asm/pgtable-bits-arcv2.h
@@ -32,6 +32,8 @@
 #define _PAGE_HW_SZ		0
 #endif
 
+#define _PAGE_TABLE		0x3
+
 /* Defaults for every user page */
 #define ___DEF		(_PAGE_PRESENT | _PAGE_CACHEABLE)
 
diff --git a/arch/arc/include/asm/pgtable-levels.h b/arch/arc/include/asm/pgtable-levels.h
index 2da3c4e52a91..6c7a8360d986 100644
--- a/arch/arc/include/asm/pgtable-levels.h
+++ b/arch/arc/include/asm/pgtable-levels.h
@@ -98,7 +98,7 @@
 
 /* In 4 level paging, p4d_* macros work on pgd */
 #define p4d_none(x)		(!p4d_val(x))
-#define p4d_bad(x)		((p4d_val(x) & ~PAGE_MASK))
+#define p4d_bad(x)		(!(p4d_val(x) & _PAGE_TABLE))
 #define p4d_present(x)		(p4d_val(x))
 #define p4d_clear(xp)		do { p4d_val(*(xp)) = 0; } while (0)
 #define p4d_pgtable(p4d)	((pud_t *)(p4d_val(p4d) & PAGE_MASK))
@@ -120,7 +120,7 @@
  * In 4 level paging, pud_* macros work on pud
  */
 #define pud_none(x)		(!pud_val(x))
-#define pud_bad(x)		((pud_val(x) & ~PAGE_MASK))
+#define pud_bad(x)		(!(pud_val(x) & _PAGE_TABLE))
 #define pud_present(x)		(pud_val(x))
 #define pud_clear(xp)		do { pud_val(*(xp)) = 0; } while (0)
 #define pud_pgtable(pud)	((pmd_t *)(pud_val(pud) & PAGE_MASK))
@@ -147,7 +147,7 @@
  * In 3+ level paging (pgd -> pmd -> pte), pmd_* macros work on pmd
  */
 #define pmd_none(x)		(!pmd_val(x))
-#define pmd_bad(x)		((pmd_val(x) & ~PAGE_MASK))
+#define pmd_bad(pmd)		(!(pmd_val(pmd) & _PAGE_TABLE))
 #define pmd_present(x)		(pmd_val(x))
 #define pmd_clear(xp)		do { pmd_val(*(xp)) = 0; } while (0)
 #define pmd_page_vaddr(pmd)	(pmd_val(pmd) & PAGE_MASK)
diff --git a/arch/arc/mm/tlbex.S b/arch/arc/mm/tlbex.S
index e054780a8fe0..3874a8086591 100644
--- a/arch/arc/mm/tlbex.S
+++ b/arch/arc/mm/tlbex.S
@@ -171,11 +171,12 @@ ex_saved_reg1:
 	lsr     r0, r2, PGDIR_SHIFT     ; Bits for indexing into PGD
 	ld.as   r3, [r1, r0]            ; PGD entry corresp to faulting addr
 	tst	r3, r3
-	bz	do_slow_path_pf         ; if no Page Table, do page fault
+	bz	do_slow_path_pf         ; next level table missing, handover to linux vm code
 
 #if CONFIG_PGTABLE_LEVELS > 3
 	lsr     r0, r2, PUD_SHIFT	; Bits for indexing into PUD
 	and	r0, r0, (PTRS_PER_PUD - 1)
+	bmskn	r3, r3, 1		; clear _PAGE_TABLE bits
 	ld.as	r1, [r3, r0]		; PMD entry
 	tst	r1, r1
 	bz	do_slow_path_pf
@@ -185,6 +186,7 @@ ex_saved_reg1:
 #if CONFIG_PGTABLE_LEVELS > 2
 	lsr     r0, r2, PMD_SHIFT	; Bits for indexing into PMD
 	and	r0, r0, (PTRS_PER_PMD - 1)
+	bmskn	r3, r3, 1		; clear _PAGE_TABLE bits
 	ld.as	r1, [r3, r0]		; PMD entry
 	tst	r1, r1
 	bz	do_slow_path_pf
-- 
2.25.1