Split ptep_establish into "establish" and "update_access_flags"

ptep_establish() is used to establish a new mapping at COW time,
and it always replaces a non-writable page mapping with a totally
new page mapping that is dirty (and likely writable, although ptrace
may cause a non-writable new mapping). Because it was nonwritable,
we don't have to worry about losing concurrent dirty page bit updates.

ptep_update_access_flags() leaves the same page mapping, but updates
the accessed/dirty/writable bits (it only ever sets them, and never
removes any permissions). Often easier, but it may race with a dirty
bit update on another CPU.

Booted on x86 and ppc64.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/asm-generic/pgtable.h

@@ -2,22 +2,34 @@
 #define _ASM_GENERIC_PGTABLE_H
 
 #ifndef __HAVE_ARCH_PTEP_ESTABLISH
-
-#ifndef ptep_update_dirty_accessed
-#define ptep_update_dirty_accessed(__ptep, __entry, __dirty) set_pte(__ptep, __entry)
-#endif
-
 /*
  * Establish a new mapping:
  *  - flush the old one
  *  - update the page tables
  *  - inform the TLB about the new one
  *
- * We hold the mm semaphore for reading and vma->vm_mm->page_table_lock
+ * We hold the mm semaphore for reading and vma->vm_mm->page_table_lock.
+ *
+ * Note: the old pte is known to not be writable, so we don't need to
+ * worry about dirty bits etc getting lost.
+ */
+#define ptep_establish(__vma, __address, __ptep, __entry)		\
+do {				  					\
+	set_pte(__ptep, __entry);					\
+	flush_tlb_page(__vma, __address);				\
+} while (0)
+#endif
+
+#ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
+/*
+ * Largely same as above, but only sets the access flags (dirty,
+ * accessed, and writable). Furthermore, we know it always gets set
+ * to a "more permissive" setting, which allows most architectures
+ * to optimize this.
  */
-#define ptep_establish(__vma, __address, __ptep, __entry, __dirty)	\
+#define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
 do {				  					  \
-	ptep_update_dirty_accessed(__ptep, __entry, __dirty);		\
+	set_pte(__ptep, __entry);					  \
 	flush_tlb_page(__vma, __address);				  \
 } while (0)
 #endif

include/asm-i386/pgtable.h

@@ -325,9 +325,13 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
  * bit at the same time.
  */
 #define update_mmu_cache(vma,address,pte) do { } while (0)
-#define ptep_update_dirty_accessed(__ptep, __entry, __dirty)	\
+#define  __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
+#define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
 	do {								  \
-		if (__dirty) set_pte(__ptep, __entry);		\
+		if (__dirty) {						  \
+			(__ptep)->pte_low = (__entry).pte_low;	  	  \
+			flush_tlb_page(__vma, __address);		  \
+		}							  \
 	} while (0)
 
 /* Encode and de-code a swap entry */

include/asm-ppc/pgtable.h

@@ -548,6 +548,16 @@ static inline void ptep_mkdirty(pte_t *ptep)
 	pte_update(ptep, 0, _PAGE_DIRTY);
 }
 
+#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
+static inline void __ptep_set_access_flags(pte_t *ptep, pte_t entry, int dirty)
+{
+	unsigned long bits = pte_val(entry) &
+		(_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW);
+	pte_update(ptep, 0, bits);
+}
+#define  ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
+        __ptep_set_access_flags(__ptep, __entry, __dirty)
+
 /*
  * Macro to mark a page protection value as "uncacheable".
  */

include/asm-ppc64/pgtable.h

@@ -306,7 +306,10 @@ static inline unsigned long pte_update(pte_t *p, unsigned long clr)
 	return old;
 }
 
-/* PTE updating functions */
+/* PTE updating functions, this function puts the PTE in the
+ * batch, doesn't actually triggers the hash flush immediately,
+ * you need to call flush_tlb_pending() to do that.
+ */
 extern void hpte_update(pte_t *ptep, unsigned long pte, int wrprot);
 
 static inline int ptep_test_and_clear_young(pte_t *ptep)
@@ -318,7 +321,7 @@ static inline int ptep_test_and_clear_young(pte_t *ptep)
 	old = pte_update(ptep, _PAGE_ACCESSED);
 	if (old & _PAGE_HASHPTE) {
 		hpte_update(ptep, old, 0);
-		flush_tlb_pending();	/* XXX generic code doesn't flush */
+		flush_tlb_pending();
 	}
 	return (old & _PAGE_ACCESSED) != 0;
 }
@@ -396,11 +399,37 @@ static inline void pte_clear(pte_t * ptep)
  */
 static inline void set_pte(pte_t *ptep, pte_t pte)
 {
-	if (pte_present(*ptep))
+	if (pte_present(*ptep)) {
 		pte_clear(ptep);
+		flush_tlb_pending();
+	}
 	*ptep = __pte(pte_val(pte)) & ~_PAGE_HPTEFLAGS;
 }
 
+/* Set the dirty and/or accessed bits atomically in a linux PTE, this
+ * function doesn't need to flush the hash entry
+ */
+#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
+static inline void __ptep_set_access_flags(pte_t *ptep, pte_t entry, int dirty)
+{
+	unsigned long bits = pte_val(entry) &
+		(_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW);
+	unsigned long old, tmp;
+
+	__asm__ __volatile__(
+	"1:	ldarx	%0,0,%4\n\
+		andi.	%1,%0,%6\n\
+		bne-	1b \n\
+		or	%0,%3,%0\n\
+		stdcx.	%0,0,%4\n\
+		bne-	1b"
+	:"=&r" (old), "=&r" (tmp), "=m" (*ptep)
+	:"r" (bits), "r" (ptep), "m" (ptep), "i" (_PAGE_BUSY)
+	:"cc");
+}
+#define  ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
+        __ptep_set_access_flags(__ptep, __entry, __dirty)
+
 /*
  * Macro to mark a page protection value as "uncacheable".
  */

include/asm-s390/pgtable.h

@@ -581,7 +581,7 @@ static inline void ptep_mkdirty(pte_t *ptep)
 static inline void
 ptep_establish(struct vm_area_struct *vma, 
 	       unsigned long address, pte_t *ptep,
-	       pte_t entry, int dirty)
+	       pte_t entry)
 {
 	ptep_clear_flush(vma, address, ptep);
 	set_pte(ptep, entry);

mm/memory.c

@@ -1004,7 +1004,7 @@ static inline void break_cow(struct vm_area_struct * vma, struct page * new_page
 	flush_cache_page(vma, address);
 	entry = maybe_mkwrite(pte_mkdirty(mk_pte(new_page, vma->vm_page_prot)),
 			      vma);
-	ptep_establish(vma, address, page_table, entry, 1);
+	ptep_establish(vma, address, page_table, entry);
 	update_mmu_cache(vma, address, entry);
 }
 
@@ -1056,7 +1056,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma,
 			flush_cache_page(vma, address);
 			entry = maybe_mkwrite(pte_mkyoung(pte_mkdirty(pte)),
 					      vma);
-			ptep_establish(vma, address, page_table, entry, 1);
+			ptep_set_access_flags(vma, address, page_table, entry, 1);
 			update_mmu_cache(vma, address, entry);
 			pte_unmap(page_table);
 			spin_unlock(&mm->page_table_lock);
@@ -1646,7 +1646,7 @@ static inline int handle_pte_fault(struct mm_struct *mm,
 		entry = pte_mkdirty(entry);
 	}
 	entry = pte_mkyoung(entry);
-	ptep_establish(vma, address, pte, entry, write_access);
+	ptep_set_access_flags(vma, address, pte, entry, write_access);
 	update_mmu_cache(vma, address, entry);
 	pte_unmap(pte);
 	spin_unlock(&mm->page_table_lock);