s390/mm: implement software referenced bits

The last remaining use for the storage key of the s390 architecture
is reference counting. The alternative is to make page table entries
invalid while they are old. On access the fault handler marks the
pte/pmd as young which makes the pte/pmd valid if the access rights
allow read access. The pte/pmd invalidations required for software
managed reference bits cost a bit of performance, on the other hand
the RRBE/RRBM instructions to read and reset the referenced bits are
quite expensive as well.

Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

7 files changed, 244 insertions, 194 deletions

diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h
index 27f04801ec8b..1e51f2915b2e 100644
--- a/arch/s390/include/asm/page.h
+++ b/arch/s390/include/asm/page.h
@@ -140,15 +140,6 @@ static inline int page_reset_referenced(unsigned long addr)
 #define _PAGE_FP_BIT		0x08	/* HW fetch protection bit	*/
 #define _PAGE_ACC_BITS		0xf0	/* HW access control bits	*/
 
-/*
- * Test and clear referenced bit in storage key.
- */
-#define __HAVE_ARCH_PAGE_TEST_AND_CLEAR_YOUNG
-static inline int page_test_and_clear_young(unsigned long pfn)
-{
-	return page_reset_referenced(pfn << PAGE_SHIFT);
-}
-
 struct page;
 void arch_free_page(struct page *page, int order);
 void arch_alloc_page(struct page *page, int order);
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 1d144b6f3ba2..9f215b40109e 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -226,8 +226,9 @@ extern unsigned long MODULES_END;
 #define _PAGE_TYPE	0x002		/* SW pte type bit */
 #define _PAGE_YOUNG	0x004		/* SW pte young bit */
 #define _PAGE_DIRTY	0x008		/* SW pte dirty bit */
-#define _PAGE_WRITE	0x010		/* SW pte write bit */
-#define _PAGE_SPECIAL	0x020		/* SW associated with special page */
+#define _PAGE_READ	0x010		/* SW pte read bit */
+#define _PAGE_WRITE	0x020		/* SW pte write bit */
+#define _PAGE_SPECIAL	0x040		/* SW associated with special page */
 #define __HAVE_ARCH_PTE_SPECIAL
 
 /* Set of bits not changed in pte_modify */
@@ -243,19 +244,25 @@ extern unsigned long MODULES_END;
  * The following table gives the different possible bit combinations for
  * the pte hardware and software bits in the last 12 bits of a pte:
  *
- *			842100000000
- *			000084210000
- *			000000008421
- *			.IR....wdytp
- * empty		.10....00000
- * swap			.10....xxx10
- * file			.11....xxxx0
- * prot-none, clean	.11....00x01
- * prot-none, dirty	.10....01x01
- * read-only, clean	.01....00x01
- * read-only, dirty	.01....01x01
- * read-write, clean	.01....10x01
- * read-write, dirty	.00....11x01
+ *				842100000000
+ *				000084210000
+ *				000000008421
+ *				.IR...wrdytp
+ * empty			.10...000000
+ * swap				.10...xxxx10
+ * file				.11...xxxxx0
+ * prot-none, clean, old	.11...000001
+ * prot-none, clean, young	.11...000101
+ * prot-none, dirty, old	.10...001001
+ * prot-none, dirty, young	.10...001101
+ * read-only, clean, old	.11...010001
+ * read-only, clean, young	.01...010101
+ * read-only, dirty, old	.11...011001
+ * read-only, dirty, young	.01...011101
+ * read-write, clean, old	.11...110001
+ * read-write, clean, young	.01...110101
+ * read-write, dirty, old	.10...111001
+ * read-write, dirty, young	.00...111101
  *
  * pte_present is true for the bit pattern .xx...xxxxx1, (pte & 0x001) == 0x001
  * pte_none    is true for the bit pattern .10...xxxx00, (pte & 0x603) == 0x400
@@ -273,15 +280,26 @@ extern unsigned long MODULES_END;
 #define _ASCE_TABLE_LENGTH	0x7f	/* 128 x 64 entries = 8k	    */
 
 /* Bits in the segment table entry */
+#define _SEGMENT_ENTRY_BITS	0x7fffffffUL	/* Valid segment table bits */
 #define _SEGMENT_ENTRY_ORIGIN	0x7fffffc0UL	/* page table origin	    */
 #define _SEGMENT_ENTRY_PROTECT	0x200	/* page protection bit		    */
 #define _SEGMENT_ENTRY_INVALID	0x20	/* invalid segment table entry	    */
 #define _SEGMENT_ENTRY_COMMON	0x10	/* common segment bit		    */
 #define _SEGMENT_ENTRY_PTL	0x0f	/* page table length		    */
+#define _SEGMENT_ENTRY_NONE	_SEGMENT_ENTRY_PROTECT
 
 #define _SEGMENT_ENTRY		(_SEGMENT_ENTRY_PTL)
 #define _SEGMENT_ENTRY_EMPTY	(_SEGMENT_ENTRY_INVALID)
 
+/*
+ * Segment table entry encoding (I = invalid, R = read-only bit):
+ *		..R...I.....
+ * prot-none	..1...1.....
+ * read-only	..1...0.....
+ * read-write	..0...0.....
+ * empty	..0...1.....
+ */
+
 /* Page status table bits for virtualization */
 #define PGSTE_ACC_BITS	0xf0000000UL
 #define PGSTE_FP_BIT	0x08000000UL
@@ -290,9 +308,7 @@ extern unsigned long MODULES_END;
 #define PGSTE_HC_BIT	0x00200000UL
 #define PGSTE_GR_BIT	0x00040000UL
 #define PGSTE_GC_BIT	0x00020000UL
-#define PGSTE_UR_BIT	0x00008000UL
-#define PGSTE_UC_BIT	0x00004000UL	/* user dirty (migration) */
-#define PGSTE_IN_BIT	0x00002000UL	/* IPTE notify bit */
+#define PGSTE_IN_BIT	0x00008000UL	/* IPTE notify bit */
 
 #else /* CONFIG_64BIT */
 
@@ -331,6 +347,8 @@ extern unsigned long MODULES_END;
 #define _REGION3_ENTRY_CO	0x100	/* change-recording override	    */
 
 /* Bits in the segment table entry */
+#define _SEGMENT_ENTRY_BITS	0xfffffffffffffe33UL
+#define _SEGMENT_ENTRY_BITS_LARGE 0xfffffffffff1ff33UL
 #define _SEGMENT_ENTRY_ORIGIN_LARGE ~0xfffffUL /* large page address	    */
 #define _SEGMENT_ENTRY_ORIGIN	~0x7ffUL/* segment table origin		    */
 #define _SEGMENT_ENTRY_PROTECT	0x200	/* page protection bit		    */
@@ -342,6 +360,21 @@ extern unsigned long MODULES_END;
 #define _SEGMENT_ENTRY_LARGE	0x400	/* STE-format control, large page   */
 #define _SEGMENT_ENTRY_CO	0x100	/* change-recording override   */
 #define _SEGMENT_ENTRY_SPLIT	0x001	/* THP splitting bit */
+#define _SEGMENT_ENTRY_YOUNG	0x002	/* SW segment young bit */
+#define _SEGMENT_ENTRY_NONE	_SEGMENT_ENTRY_YOUNG
+
+/*
+ * Segment table entry encoding (R = read-only, I = invalid, y = young bit):
+ *			..R...I...y.
+ * prot-none, old	..0...1...1.
+ * prot-none, young	..1...1...1.
+ * read-only, old	..1...1...0.
+ * read-only, young	..1...0...1.
+ * read-write, old	..0...1...0.
+ * read-write, young	..0...0...1.
+ * The segment table origin is used to distinguish empty (origin==0) from
+ * read-write, old segment table entries (origin!=0)
+ */
 
 #define _SEGMENT_ENTRY_SPLIT_BIT 0	/* THP splitting bit number */
 
@@ -357,9 +390,7 @@ extern unsigned long MODULES_END;
 #define PGSTE_HC_BIT	0x0020000000000000UL
 #define PGSTE_GR_BIT	0x0004000000000000UL
 #define PGSTE_GC_BIT	0x0002000000000000UL
-#define PGSTE_UR_BIT	0x0000800000000000UL
-#define PGSTE_UC_BIT	0x0000400000000000UL	/* user dirty (migration) */
-#define PGSTE_IN_BIT	0x0000200000000000UL	/* IPTE notify bit */
+#define PGSTE_IN_BIT	0x0000800000000000UL	/* IPTE notify bit */
 
 #endif /* CONFIG_64BIT */
 
@@ -375,12 +406,17 @@ extern unsigned long MODULES_END;
  * Page protection definitions.
  */
 #define PAGE_NONE	__pgprot(_PAGE_PRESENT | _PAGE_INVALID)
-#define PAGE_READ	__pgprot(_PAGE_PRESENT | _PAGE_PROTECT)
-#define PAGE_WRITE	__pgprot(_PAGE_PRESENT | _PAGE_WRITE | _PAGE_PROTECT)
-
-#define PAGE_SHARED	__pgprot(_PAGE_PRESENT | _PAGE_WRITE | _PAGE_DIRTY)
-#define PAGE_KERNEL	__pgprot(_PAGE_PRESENT | _PAGE_WRITE | _PAGE_DIRTY)
-#define PAGE_KERNEL_RO	__pgprot(_PAGE_PRESENT | _PAGE_PROTECT)
+#define PAGE_READ	__pgprot(_PAGE_PRESENT | _PAGE_READ | \
+				 _PAGE_INVALID | _PAGE_PROTECT)
+#define PAGE_WRITE	__pgprot(_PAGE_PRESENT | _PAGE_READ | _PAGE_WRITE | \
+				 _PAGE_INVALID | _PAGE_PROTECT)
+
+#define PAGE_SHARED	__pgprot(_PAGE_PRESENT | _PAGE_READ | _PAGE_WRITE | \
+				 _PAGE_YOUNG | _PAGE_DIRTY)
+#define PAGE_KERNEL	__pgprot(_PAGE_PRESENT | _PAGE_READ | _PAGE_WRITE | \
+				 _PAGE_YOUNG | _PAGE_DIRTY)
+#define PAGE_KERNEL_RO	__pgprot(_PAGE_PRESENT | _PAGE_READ | _PAGE_YOUNG | \
+				 _PAGE_PROTECT)
 
 /*
  * On s390 the page table entry has an invalid bit and a read-only bit.
@@ -410,9 +446,10 @@ extern unsigned long MODULES_END;
  * Segment entry (large page) protection definitions.
  */
 #define SEGMENT_NONE	__pgprot(_SEGMENT_ENTRY_INVALID | \
+				 _SEGMENT_ENTRY_NONE)
+#define SEGMENT_READ	__pgprot(_SEGMENT_ENTRY_INVALID | \
 				 _SEGMENT_ENTRY_PROTECT)
-#define SEGMENT_READ	__pgprot(_SEGMENT_ENTRY_PROTECT)
-#define SEGMENT_WRITE	__pgprot(0)
+#define SEGMENT_WRITE	__pgprot(_SEGMENT_ENTRY_INVALID)
 
 static inline int mm_has_pgste(struct mm_struct *mm)
 {
@@ -520,10 +557,19 @@ static inline int pmd_large(pmd_t pmd)
 #endif
 }
 
+static inline int pmd_prot_none(pmd_t pmd)
+{
+	return (pmd_val(pmd) & _SEGMENT_ENTRY_INVALID) &&
+		(pmd_val(pmd) & _SEGMENT_ENTRY_NONE);
+}
+
 static inline int pmd_bad(pmd_t pmd)
 {
-	unsigned long mask = ~_SEGMENT_ENTRY_ORIGIN & ~_SEGMENT_ENTRY_INVALID;
-	return (pmd_val(pmd) & mask) != _SEGMENT_ENTRY;
+#ifdef CONFIG_64BIT
+	if (pmd_large(pmd))
+		return (pmd_val(pmd) & ~_SEGMENT_ENTRY_BITS_LARGE) != 0;
+#endif
+	return (pmd_val(pmd) & ~_SEGMENT_ENTRY_BITS) != 0;
 }
 
 #define __HAVE_ARCH_PMDP_SPLITTING_FLUSH
@@ -542,12 +588,21 @@ extern int pmdp_clear_flush_young(struct vm_area_struct *vma,
 #define __HAVE_ARCH_PMD_WRITE
 static inline int pmd_write(pmd_t pmd)
 {
+	if (pmd_prot_none(pmd))
+		return 0;
 	return (pmd_val(pmd) & _SEGMENT_ENTRY_PROTECT) == 0;
 }
 
 static inline int pmd_young(pmd_t pmd)
 {
-	return 0;
+	int young = 0;
+#ifdef CONFIG_64BIT
+	if (pmd_prot_none(pmd))
+		young = (pmd_val(pmd) & _SEGMENT_ENTRY_PROTECT) != 0;
+	else
+		young = (pmd_val(pmd) & _SEGMENT_ENTRY_YOUNG) != 0;
+#endif
+	return young;
 }
 
 static inline int pte_present(pte_t pte)
@@ -632,33 +687,28 @@ static inline void pgste_set(pte_t *ptep, pgste_t pgste)
 static inline pgste_t pgste_update_all(pte_t *ptep, pgste_t pgste)
 {
 #ifdef CONFIG_PGSTE
-	unsigned long address, bits;
-	unsigned char skey;
+	unsigned long address, bits, skey;
 
 	if (pte_val(*ptep) & _PAGE_INVALID)
 		return pgste;
 	address = pte_val(*ptep) & PAGE_MASK;
-	skey = page_get_storage_key(address);
+	skey = (unsigned long) page_get_storage_key(address);
 	bits = skey & (_PAGE_CHANGED | _PAGE_REFERENCED);
-	/* Clear page changed & referenced bit in the storage key */
-	if (bits & _PAGE_CHANGED)
+	if (!(pgste_val(pgste) & PGSTE_HC_BIT) && (bits & _PAGE_CHANGED)) {
+		/* Transfer dirty + referenced bit to host bits in pgste */
+		pgste_val(pgste) |= bits << 52;
 		page_set_storage_key(address, skey ^ bits, 0);
-	else if (bits)
+	} else if (!(pgste_val(pgste) & PGSTE_HR_BIT) &&
+		   (bits & _PAGE_REFERENCED)) {
+		/* Transfer referenced bit to host bit in pgste */
+		pgste_val(pgste) |= PGSTE_HR_BIT;
 		page_reset_referenced(address);
+	}
 	/* Transfer page changed & referenced bit to guest bits in pgste */
 	pgste_val(pgste) |= bits << 48;		/* GR bit & GC bit */
-	/* Get host changed & referenced bits from pgste */
-	bits |= (pgste_val(pgste) & (PGSTE_HR_BIT | PGSTE_HC_BIT)) >> 52;
-	/* Transfer page changed & referenced bit to kvm user bits */
-	pgste_val(pgste) |= bits << 45;		/* PGSTE_UR_BIT & PGSTE_UC_BIT */
-	/* Clear relevant host bits in pgste. */
-	pgste_val(pgste) &= ~(PGSTE_HR_BIT | PGSTE_HC_BIT);
-	pgste_val(pgste) &= ~(PGSTE_ACC_BITS | PGSTE_FP_BIT);
 	/* Copy page access key and fetch protection bit to pgste */
-	pgste_val(pgste) |=
-		(unsigned long) (skey & (_PAGE_ACC_BITS | _PAGE_FP_BIT)) << 56;
-	/* Transfer referenced bit to pte */
-	pte_val(*ptep) |= (bits & _PAGE_REFERENCED) << 1;
+	pgste_val(pgste) &= ~(PGSTE_ACC_BITS | PGSTE_FP_BIT);
+	pgste_val(pgste) |= (skey & (_PAGE_ACC_BITS | _PAGE_FP_BIT)) << 56;
 #endif
 	return pgste;
 
@@ -667,24 +717,11 @@ static inline pgste_t pgste_update_all(pte_t *ptep, pgste_t pgste)
 static inline pgste_t pgste_update_young(pte_t *ptep, pgste_t pgste)
 {
 #ifdef CONFIG_PGSTE
-	int young;
-
 	if (pte_val(*ptep) & _PAGE_INVALID)
 		return pgste;
 	/* Get referenced bit from storage key */
-	young = page_reset_referenced(pte_val(*ptep) & PAGE_MASK);
-	if (young)
-		pgste_val(pgste) |= PGSTE_GR_BIT;
-	/* Get host referenced bit from pgste */
-	if (pgste_val(pgste) & PGSTE_HR_BIT) {
-		pgste_val(pgste) &= ~PGSTE_HR_BIT;
-		young = 1;
-	}
-	/* Transfer referenced bit to kvm user bits and pte */
-	if (young) {
-		pgste_val(pgste) |= PGSTE_UR_BIT;
-		pte_val(*ptep) |= _PAGE_YOUNG;
-	}
+	if (page_reset_referenced(pte_val(*ptep) & PAGE_MASK))
+		pgste_val(pgste) |= PGSTE_HR_BIT | PGSTE_GR_BIT;
 #endif
 	return pgste;
 }
@@ -839,11 +876,7 @@ static inline int pte_dirty(pte_t pte)
 
 static inline int pte_young(pte_t pte)
 {
-#ifdef CONFIG_PGSTE
-	if (pte_val(pte) & _PAGE_YOUNG)
-		return 1;
-#endif
-	return 0;
+	return (pte_val(pte) & _PAGE_YOUNG) != 0;
 }
 
 /*
@@ -884,6 +917,16 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
 	pte_val(pte) &= _PAGE_CHG_MASK;
 	pte_val(pte) |= pgprot_val(newprot);
+	/*
+	 * newprot for PAGE_NONE, PAGE_READ and PAGE_WRITE has the
+	 * invalid bit set, clear it again for readable, young pages
+	 */
+	if ((pte_val(pte) & _PAGE_YOUNG) && (pte_val(pte) & _PAGE_READ))
+		pte_val(pte) &= ~_PAGE_INVALID;
+	/*
+	 * newprot for PAGE_READ and PAGE_WRITE has the page protection
+	 * bit set, clear it again for writable, dirty pages
+	 */
 	if ((pte_val(pte) & _PAGE_DIRTY) && (pte_val(pte) & _PAGE_WRITE))
 		pte_val(pte) &= ~_PAGE_PROTECT;
 	return pte;
@@ -921,14 +964,16 @@ static inline pte_t pte_mkdirty(pte_t pte)
 
 static inline pte_t pte_mkold(pte_t pte)
 {
-#ifdef CONFIG_PGSTE
 	pte_val(pte) &= ~_PAGE_YOUNG;
-#endif
+	pte_val(pte) |= _PAGE_INVALID;
 	return pte;
 }
 
 static inline pte_t pte_mkyoung(pte_t pte)
 {
+	pte_val(pte) |= _PAGE_YOUNG;
+	if (pte_val(pte) & _PAGE_READ)
+		pte_val(pte) &= ~_PAGE_INVALID;
 	return pte;
 }
 
@@ -958,8 +1003,8 @@ static inline int ptep_test_and_clear_user_dirty(struct mm_struct *mm,
 	if (mm_has_pgste(mm)) {
 		pgste = pgste_get_lock(ptep);
 		pgste = pgste_update_all(ptep, pgste);
-		dirty = !!(pgste_val(pgste) & PGSTE_UC_BIT);
-		pgste_val(pgste) &= ~PGSTE_UC_BIT;
+		dirty = !!(pgste_val(pgste) & PGSTE_HC_BIT);
+		pgste_val(pgste) &= ~PGSTE_HC_BIT;
 		pgste_set_unlock(ptep, pgste);
 		return dirty;
 	}
@@ -978,42 +1023,13 @@ static inline int ptep_test_and_clear_user_young(struct mm_struct *mm,
 	if (mm_has_pgste(mm)) {
 		pgste = pgste_get_lock(ptep);
 		pgste = pgste_update_young(ptep, pgste);
-		young = !!(pgste_val(pgste) & PGSTE_UR_BIT);
-		pgste_val(pgste) &= ~PGSTE_UR_BIT;
+		young = !!(pgste_val(pgste) & PGSTE_HR_BIT);
+		pgste_val(pgste) &= ~PGSTE_HR_BIT;
 		pgste_set_unlock(ptep, pgste);
 	}
 	return young;
 }
 
-#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
-static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
-					    unsigned long addr, pte_t *ptep)
-{
-	pgste_t pgste;
-	pte_t pte;
-
-	if (mm_has_pgste(vma->vm_mm)) {
-		pgste = pgste_get_lock(ptep);
-		pgste = pgste_update_young(ptep, pgste);
-		pte = *ptep;
-		*ptep = pte_mkold(pte);
-		pgste_set_unlock(ptep, pgste);
-		return pte_young(pte);
-	}
-	return 0;
-}
-
-#define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
-static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
-					 unsigned long address, pte_t *ptep)
-{
-	/* No need to flush TLB
-	 * On s390 reference bits are in storage key and never in TLB
-	 * With virtualization we handle the reference bit, without we
-	 * we can simply return */
-	return ptep_test_and_clear_young(vma, address, ptep);
-}
-
 static inline void __ptep_ipte(unsigned long address, pte_t *ptep)
 {
 	if (!(pte_val(*ptep) & _PAGE_INVALID)) {
@@ -1042,6 +1058,40 @@ static inline void ptep_flush_lazy(struct mm_struct *mm,
 		mm->context.flush_mm = 1;
 }
 
+#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
+static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
+					    unsigned long addr, pte_t *ptep)
+{
+	pgste_t pgste;
+	pte_t pte;
+	int young;
+
+	if (mm_has_pgste(vma->vm_mm)) {
+		pgste = pgste_get_lock(ptep);
+		pgste = pgste_ipte_notify(vma->vm_mm, addr, ptep, pgste);
+	}
+
+	pte = *ptep;
+	__ptep_ipte(addr, ptep);
+	young = pte_young(pte);
+	pte = pte_mkold(pte);
+
+	if (mm_has_pgste(vma->vm_mm)) {
+		pgste_set_pte(ptep, pte);
+		pgste_set_unlock(ptep, pgste);
+	} else
+		*ptep = pte;
+
+	return young;
+}
+
+#define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
+static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
+					 unsigned long address, pte_t *ptep)
+{
+	return ptep_test_and_clear_young(vma, address, ptep);
+}
+
 /*
  * This is hard to understand. ptep_get_and_clear and ptep_clear_flush
  * both clear the TLB for the unmapped pte. The reason is that
@@ -1229,7 +1279,7 @@ static inline pte_t mk_pte_phys(unsigned long physpage, pgprot_t pgprot)
 {
 	pte_t __pte;
 	pte_val(__pte) = physpage + pgprot_val(pgprot);
-	return __pte;
+	return pte_mkyoung(__pte);
 }
 
 static inline pte_t mk_pte(struct page *page, pgprot_t pgprot)
@@ -1338,10 +1388,41 @@ static inline unsigned long massage_pgprot_pmd(pgprot_t pgprot)
 	return pgprot_val(SEGMENT_WRITE);
 }
 
+static inline pmd_t pmd_mkyoung(pmd_t pmd)
+{
+#ifdef CONFIG_64BIT
+	if (pmd_prot_none(pmd)) {
+		pmd_val(pmd) |= _SEGMENT_ENTRY_PROTECT;
+	} else {
+		pmd_val(pmd) |= _SEGMENT_ENTRY_YOUNG;
+		pmd_val(pmd) &= ~_SEGMENT_ENTRY_INVALID;
+	}
+#endif
+	return pmd;
+}
+
+static inline pmd_t pmd_mkold(pmd_t pmd)
+{
+#ifdef CONFIG_64BIT
+	if (pmd_prot_none(pmd)) {
+		pmd_val(pmd) &= ~_SEGMENT_ENTRY_PROTECT;
+	} else {
+		pmd_val(pmd) &= ~_SEGMENT_ENTRY_YOUNG;
+		pmd_val(pmd) |= _SEGMENT_ENTRY_INVALID;
+	}
+#endif
+	return pmd;
+}
+
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 {
+	int young;
+
+	young = pmd_young(pmd);
 	pmd_val(pmd) &= _SEGMENT_CHG_MASK;
 	pmd_val(pmd) |= massage_pgprot_pmd(newprot);
+	if (young)
+		pmd = pmd_mkyoung(pmd);
 	return pmd;
 }
 
@@ -1349,13 +1430,13 @@ static inline pmd_t mk_pmd_phys(unsigned long physpage, pgprot_t pgprot)
 {
 	pmd_t __pmd;
 	pmd_val(__pmd) = physpage + massage_pgprot_pmd(pgprot);
-	return __pmd;
+	return pmd_mkyoung(__pmd);
 }
 
 static inline pmd_t pmd_mkwrite(pmd_t pmd)
 {
-	/* Do not clobber PROT_NONE pages! */
-	if (!(pmd_val(pmd) & _SEGMENT_ENTRY_INVALID))
+	/* Do not clobber PROT_NONE segments! */
+	if (!pmd_prot_none(pmd))
 		pmd_val(pmd) &= ~_SEGMENT_ENTRY_PROTECT;
 	return pmd;
 }
@@ -1391,7 +1472,9 @@ static inline pmd_t pmd_mkhuge(pmd_t pmd)
 
 static inline pmd_t pmd_wrprotect(pmd_t pmd)
 {
-	pmd_val(pmd) |= _SEGMENT_ENTRY_PROTECT;
+	/* Do not clobber PROT_NONE segments! */
+	if (!pmd_prot_none(pmd))
+		pmd_val(pmd) |= _SEGMENT_ENTRY_PROTECT;
 	return pmd;
 }
 
@@ -1401,50 +1484,16 @@ static inline pmd_t pmd_mkdirty(pmd_t pmd)
 	return pmd;
 }
 
-static inline pmd_t pmd_mkold(pmd_t pmd)
-{
-	/* No referenced bit in the segment table entry. */
-	return pmd;
-}
-
-static inline pmd_t pmd_mkyoung(pmd_t pmd)
-{
-	/* No referenced bit in the segment table entry. */
-	return pmd;
-}
-
 #define __HAVE_ARCH_PMDP_TEST_AND_CLEAR_YOUNG
 static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 					    unsigned long address, pmd_t *pmdp)
 {
-	unsigned long pmd_addr = pmd_val(*pmdp) & HPAGE_MASK;
-	long tmp, rc;
-	int counter;
+	pmd_t pmd;
 
-	rc = 0;
-	if (MACHINE_HAS_RRBM) {
-		counter = PTRS_PER_PTE >> 6;
-		asm volatile(
-			"0:	.insn	rre,0xb9ae0000,%0,%3\n"	/* rrbm */
-			"	ogr	%1,%0\n"
-			"	la	%3,0(%4,%3)\n"
-			"	brct	%2,0b\n"
-			: "=&d" (tmp), "+&d" (rc), "+d" (counter),
-			  "+a" (pmd_addr)
-			: "a" (64 * 4096UL) : "cc");
-		rc = !!rc;
-	} else {
-		counter = PTRS_PER_PTE;
-		asm volatile(
-			"0:	rrbe	0,%2\n"
-			"	la	%2,0(%3,%2)\n"
-			"	brc	12,1f\n"
-			"	lhi	%0,1\n"
-			"1:	brct	%1,0b\n"
-			: "+d" (rc), "+d" (counter), "+a" (pmd_addr)
-			: "a" (4096UL) : "cc");
-	}
-	return rc;
+	pmd = *pmdp;
+	__pmd_idte(address, pmdp);
+	*pmdp = pmd_mkold(pmd);
+	return pmd_young(pmd);
 }
 
 #define __HAVE_ARCH_PMDP_GET_AND_CLEAR
diff --git a/arch/s390/mm/hugetlbpage.c b/arch/s390/mm/hugetlbpage.c
index b0bd0ae17796..248445f92604 100644
--- a/arch/s390/mm/hugetlbpage.c
+++ b/arch/s390/mm/hugetlbpage.c
@@ -10,19 +10,25 @@
 
 static inline pmd_t __pte_to_pmd(pte_t pte)
 {
-	int none, prot;
+	int none, young, prot;
 	pmd_t pmd;
 
 	/*
-	 * Convert encoding	  pte bits	  pmd bits
-	 *			.IR.....wdtp	..R...I.....
-	 * empty		.10.....0000 -> ..0...1.....
-	 * prot-none, clean	.11.....0001 -> ..1...1.....
-	 * prot-none, dirty	.10.....0101 -> ..1...1.....
-	 * read-only, clean	.01.....0001 -> ..1...0.....
-	 * read-only, dirty	.01.....0101 -> ..1...0.....
-	 * read-write, clean	.01.....1001 -> ..0...0.....
-	 * read-write, dirty	.00.....1101 -> ..0...0.....
+	 * Convert encoding		  pte bits	  pmd bits
+	 *				.IR...wrdytp	..R...I...y.
+	 * empty			.10...000000 -> ..0...1...0.
+	 * prot-none, clean, old	.11...000001 -> ..0...1...1.
+	 * prot-none, clean, young	.11...000101 -> ..1...1...1.
+	 * prot-none, dirty, old	.10...001001 -> ..0...1...1.
+	 * prot-none, dirty, young	.10...001101 -> ..1...1...1.
+	 * read-only, clean, old	.11...010001 -> ..1...1...0.
+	 * read-only, clean, young	.01...010101 -> ..1...0...1.
+	 * read-only, dirty, old	.11...011001 -> ..1...1...0.
+	 * read-only, dirty, young	.01...011101 -> ..1...0...1.
+	 * read-write, clean, old	.11...110001 -> ..0...1...0.
+	 * read-write, clean, young	.01...110101 -> ..0...0...1.
+	 * read-write, dirty, old	.10...111001 -> ..0...1...0.
+	 * read-write, dirty, young	.00...111101 -> ..0...0...1.
 	 * Huge ptes are dirty by definition, a clean pte is made dirty
 	 * by the conversion.
 	 */
@@ -31,9 +37,14 @@ static inline pmd_t __pte_to_pmd(pte_t pte)
 		if (pte_val(pte) & _PAGE_INVALID)
 			pmd_val(pmd) |= _SEGMENT_ENTRY_INVALID;
 		none = (pte_val(pte) & _PAGE_PRESENT) &&
-			(pte_val(pte) & _PAGE_INVALID);
-		prot = (pte_val(pte) & _PAGE_PROTECT);
-		if (prot || none)
+			!(pte_val(pte) & _PAGE_READ) &&
+			!(pte_val(pte) & _PAGE_WRITE);
+		prot = (pte_val(pte) & _PAGE_PROTECT) &&
+			!(pte_val(pte) & _PAGE_WRITE);
+		young = pte_val(pte) & _PAGE_YOUNG;
+		if (none || young)
+			pmd_val(pmd) |= _SEGMENT_ENTRY_YOUNG;
+		if (prot || (none && young))
 			pmd_val(pmd) |= _SEGMENT_ENTRY_PROTECT;
 	} else
 		pmd_val(pmd) = _SEGMENT_ENTRY_INVALID;
@@ -46,11 +57,14 @@ static inline pte_t __pmd_to_pte(pmd_t pmd)
 
 	/*
 	 * Convert encoding	  pmd bits	  pte bits
-	 *			..R...I.....	.IR.....wdtp
-	 * empty		..0...1..... -> .10.....0000
-	 * prot-none, young	..1...1..... -> .10.....0101
-	 * read-only, young	..1...0..... -> .01.....0101
-	 * read-write, young	..0...0..... -> .00.....1101
+	 *			..R...I...y.	.IR...wrdytp
+	 * empty		..0...1...0. -> .10...000000
+	 * prot-none, old	..0...1...1. -> .10...001001
+	 * prot-none, young	..1...1...1. -> .10...001101
+	 * read-only, old	..1...1...0. -> .11...011001
+	 * read-only, young	..1...0...1. -> .01...011101
+	 * read-write, old	..0...1...0. -> .10...111001
+	 * read-write, young	..0...0...1. -> .00...111101
 	 * Huge ptes are dirty by definition
 	 */
 	if (pmd_present(pmd)) {
@@ -58,11 +72,17 @@ static inline pte_t __pmd_to_pte(pmd_t pmd)
 			(pmd_val(pmd) & PAGE_MASK);
 		if (pmd_val(pmd) & _SEGMENT_ENTRY_INVALID)
 			pte_val(pte) |= _PAGE_INVALID;
-		else {
+		if (pmd_prot_none(pmd)) {
+			if (pmd_val(pmd) & _SEGMENT_ENTRY_PROTECT)
+				pte_val(pte) |= _PAGE_YOUNG;
+		} else {
+			pte_val(pte) |= _PAGE_READ;
 			if (pmd_val(pmd) & _SEGMENT_ENTRY_PROTECT)
 				pte_val(pte) |= _PAGE_PROTECT;
 			else
 				pte_val(pte) |= _PAGE_WRITE;
+			if (pmd_val(pmd) & _SEGMENT_ENTRY_YOUNG)
+				pte_val(pte) |= _PAGE_YOUNG;
 		}
 	} else
 		pte_val(pte) = _PAGE_INVALID;
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index befaea7003f7..6d16132d0850 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -754,7 +754,8 @@ static inline unsigned long *page_table_alloc_pgste(struct mm_struct *mm,
 	atomic_set(&page->_mapcount, 3);
 	table = (unsigned long *) page_to_phys(page);
 	clear_table(table, _PAGE_INVALID, PAGE_SIZE/2);
-	clear_table(table + PTRS_PER_PTE, 0, PAGE_SIZE/2);
+	clear_table(table + PTRS_PER_PTE, PGSTE_HR_BIT | PGSTE_HC_BIT,
+		    PAGE_SIZE/2);
 	return table;
 }
 
@@ -792,26 +793,21 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
 	pgste_val(new) |= (key & (_PAGE_CHANGED | _PAGE_REFERENCED)) << 48;
 	pgste_val(new) |= (key & (_PAGE_ACC_BITS | _PAGE_FP_BIT)) << 56;
 	if (!(pte_val(*ptep) & _PAGE_INVALID)) {
-		unsigned long address, bits;
-		unsigned char skey;
+		unsigned long address, bits, skey;
 
 		address = pte_val(*ptep) & PAGE_MASK;
-		skey = page_get_storage_key(address);
+		skey = (unsigned long) page_get_storage_key(address);
 		bits = skey & (_PAGE_CHANGED | _PAGE_REFERENCED);
+		skey = key & (_PAGE_ACC_BITS | _PAGE_FP_BIT);
 		/* Set storage key ACC and FP */
-		page_set_storage_key(address,
-				(key & (_PAGE_ACC_BITS | _PAGE_FP_BIT)),
-				!nq);
-
+		page_set_storage_key(address, skey, !nq);
 		/* Merge host changed & referenced into pgste  */
 		pgste_val(new) |= bits << 52;
-		/* Transfer skey changed & referenced bit to kvm user bits */
-		pgste_val(new) |= bits << 45;	/* PGSTE_UR_BIT & PGSTE_UC_BIT */
 	}
 	/* changing the guest storage key is considered a change of the page */
 	if ((pgste_val(new) ^ pgste_val(old)) &
 	    (PGSTE_ACC_BITS | PGSTE_FP_BIT | PGSTE_GR_BIT | PGSTE_GC_BIT))
-		pgste_val(new) |= PGSTE_UC_BIT;
+		pgste_val(new) |= PGSTE_HC_BIT;
 
 	pgste_set_unlock(ptep, new);
 	pte_unmap_unlock(*ptep, ptl);
diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index e1299d40818d..bcfb70b60be6 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -118,6 +118,7 @@ static int vmem_add_mem(unsigned long start, unsigned long size, int ro)
 		    !(address & ~PMD_MASK) && (address + PMD_SIZE <= end)) {
 			pmd_val(*pm_dir) = __pa(address) |
 				_SEGMENT_ENTRY | _SEGMENT_ENTRY_LARGE |
+				_SEGMENT_ENTRY_YOUNG |
 				(ro ? _SEGMENT_ENTRY_PROTECT : 0);
 			address += PMD_SIZE;
 			continue;
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 0807ddf97b05..f330d28e4d0e 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -208,10 +208,6 @@ static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
-#ifndef __HAVE_ARCH_PAGE_TEST_AND_CLEAR_YOUNG
-#define page_test_and_clear_young(pfn) (0)
-#endif
-
 #ifndef __HAVE_ARCH_PGD_OFFSET_GATE
 #define pgd_offset_gate(mm, addr)	pgd_offset(mm, addr)
 #endif
diff --git a/mm/rmap.c b/mm/rmap.c
index b2e29acd7e3d..07748e68b729 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -873,9 +873,6 @@ int page_referenced(struct page *page,
 								vm_flags);
 		if (we_locked)
 			unlock_page(page);
-
-		if (page_test_and_clear_young(page_to_pfn(page)))
-			referenced++;
 	}
 out:
 	return referenced;