Subject: [PATCH/RFC] Rework ptep_set_access_flags and fix sun4c

From: Benjamin Herrenschmidt <[email-masked]>
Date: Tue, 22 May 2007 16:28:59 +1000

This patch reworks ptep_set_access_flags() and the callers so that the
comparison to the old PTE is done inside that function, which then
returns wether an update_mmu_cache() is needed. That allows fixing
the sun4c situation where update_mmu_cache() needs to be forced,
always.

Signed-off-by: Benjamin Herrenschmidt <[email-masked]>
---

Ok, so that's only compile tested on sparc32 and powerpc 32 bits, boot
tested on powerpc64 and not tested on others (I could use some help
testing x86, x86_64 and s390 who also have their own implementations).

Index: linux-work/include/asm-generic/pgtable.h
===================================================================
--- linux-work.orig/include/asm-generic/pgtable.h	2007-05-22 15:04:45.000000000 +1000
+++ linux-work/include/asm-generic/pgtable.h	2007-05-22 15:32:21.000000000 +1000
@@ -27,13 +27,20 @@ do {				  					\
  * 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.
+ * to optimize this. We return wether the PTE actually changed, which
+ * in turn instructs the caller to do things like update__mmu_cache.
+ * This used to be done in the caller, but sparc needs minor faults to
+ * force that call on sun4c so we changed this macro slightly
  */
 #define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
-do {				  					  \
-	set_pte_at((__vma)->vm_mm, (__address), __ptep, __entry);	  \
-	flush_tlb_page(__vma, __address);				  \
-} while (0)
+({									  \
+	int __changed = !pte_same(*(__ptep), __entry);			  \
+	if (__changed) {						  \
+		set_pte_at((__vma)->vm_mm, (__address), __ptep, __entry); \
+		flush_tlb_page(__vma, __address);			  \
+	}								  \
+	__changed;							  \
+})
 #endif
 
 #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
Index: linux-work/include/asm-powerpc/pgtable-ppc64.h
===================================================================
--- linux-work.orig/include/asm-powerpc/pgtable-ppc64.h	2007-05-22 15:04:45.000000000 +1000
+++ linux-work/include/asm-powerpc/pgtable-ppc64.h	2007-05-22 15:27:21.000000000 +1000
@@ -413,10 +413,14 @@ static inline void __ptep_set_access_fla
 	:"cc");
 }
 #define  ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
-	do {								   \
-		__ptep_set_access_flags(__ptep, __entry, __dirty);	   \
-		flush_tlb_page_nohash(__vma, __address);	       	   \
-	} while(0)
+({									   \
+	int __changed = !pte_same(*(__ptep), __entry);			   \
+	if (__changed) {						   \
+		__ptep_set_access_flags(__ptep, __entry, __dirty);    	   \
+		flush_tlb_page_nohash(__vma, __address);		   \
+	}								   \
+	__changed;							   \
+})
 
 /*
  * Macro to mark a page protection value as "uncacheable".
Index: linux-work/mm/memory.c
===================================================================
--- linux-work.orig/mm/memory.c	2007-05-22 15:04:45.000000000 +1000
+++ linux-work/mm/memory.c	2007-05-22 15:38:19.000000000 +1000
@@ -1691,9 +1691,10 @@ static int do_wp_page(struct mm_struct *
 		flush_cache_page(vma, address, pte_pfn(orig_pte));
 		entry = pte_mkyoung(orig_pte);
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
-		ptep_set_access_flags(vma, address, page_table, entry, 1);
-		update_mmu_cache(vma, address, entry);
-		lazy_mmu_prot_update(entry);
+		if (ptep_set_access_flags(vma, address, page_table, entry,1)) {
+			update_mmu_cache(vma, address, entry);
+			lazy_mmu_prot_update(entry);
+		}
 		ret |= VM_FAULT_WRITE;
 		goto unlock;
 	}
@@ -2525,10 +2526,9 @@ static inline int handle_pte_fault(struc
 		pte_t *pte, pmd_t *pmd, int write_access)
 {
 	pte_t entry;
-	pte_t old_entry;
 	spinlock_t *ptl;
 
-	old_entry = entry = *pte;
+	entry = *pte;
 	if (!pte_present(entry)) {
 		if (pte_none(entry)) {
 			if (vma->vm_ops) {
@@ -2561,8 +2561,7 @@ static inline int handle_pte_fault(struc
 		entry = pte_mkdirty(entry);
 	}
 	entry = pte_mkyoung(entry);
-	if (!pte_same(old_entry, entry)) {
-		ptep_set_access_flags(vma, address, pte, entry, write_access);
+	if (ptep_set_access_flags(vma, address, pte, entry, write_access)) {
 		update_mmu_cache(vma, address, entry);
 		lazy_mmu_prot_update(entry);
 	} else {
Index: linux-work/include/asm-powerpc/pgtable-ppc32.h
===================================================================
--- linux-work.orig/include/asm-powerpc/pgtable-ppc32.h	2007-05-22 15:04:45.000000000 +1000
+++ linux-work/include/asm-powerpc/pgtable-ppc32.h	2007-05-22 15:26:07.000000000 +1000
@@ -673,10 +673,14 @@ static inline void __ptep_set_access_fla
 }
 
 #define  ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
-	do {								   \
-		__ptep_set_access_flags(__ptep, __entry, __dirty);	   \
-		flush_tlb_page_nohash(__vma, __address);	       	   \
-	} while(0)
+({									   \
+	int __changed = !pte_same(*(__ptep), __entry);			   \
+	if (__changed) {						   \
+		__ptep_set_access_flags(__ptep, __entry, __dirty);    	   \
+		flush_tlb_page_nohash(__vma, __address);		   \
+	}								   \
+	__changed;							   \
+})
 
 /*
  * Macro to mark a page protection value as "uncacheable".
Index: linux-work/include/asm-i386/pgtable.h
===================================================================
--- linux-work.orig/include/asm-i386/pgtable.h	2007-05-22 15:06:17.000000000 +1000
+++ linux-work/include/asm-i386/pgtable.h	2007-05-22 15:16:11.000000000 +1000
@@ -285,13 +285,15 @@ static inline pte_t native_local_ptep_ge
  */
 #define  __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
 #define ptep_set_access_flags(vma, address, ptep, entry, dirty)		\
-do {									\
-	if (dirty) {							\
+({									\
+	int __changed = !pte_same(*(__ptep), __entry);			\
+	if (__changed && dirty) {					\
 		(ptep)->pte_low = (entry).pte_low;			\
 		pte_update_defer((vma)->vm_mm, (address), (ptep));	\
 		flush_tlb_page(vma, address);				\
 	}								\
-} while (0)
+	__changed;							\
+})
 
 #define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_DIRTY
 #define ptep_test_and_clear_dirty(vma, addr, ptep) ({			\
Index: linux-work/include/asm-ppc/pgtable.h
===================================================================
--- linux-work.orig/include/asm-ppc/pgtable.h	2007-05-22 15:25:58.000000000 +1000
+++ linux-work/include/asm-ppc/pgtable.h	2007-05-22 15:26:08.000000000 +1000
@@ -694,10 +694,14 @@ static inline void __ptep_set_access_fla
 }
 
 #define  ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
-	do {								   \
-		__ptep_set_access_flags(__ptep, __entry, __dirty);	   \
-		flush_tlb_page_nohash(__vma, __address);	       	   \
-	} while(0)
+({									   \
+	int __changed = !pte_same(*(__ptep), __entry);			   \
+	if (__changed) {						   \
+		__ptep_set_access_flags(__ptep, __entry, __dirty);    	   \
+		flush_tlb_page_nohash(__vma, __address);		   \
+	}								   \
+	__changed;							   \
+})
 
 /*
  * Macro to mark a page protection value as "uncacheable".
Index: linux-work/include/asm-s390/pgtable.h
===================================================================
--- linux-work.orig/include/asm-s390/pgtable.h	2007-05-22 15:16:48.000000000 +1000
+++ linux-work/include/asm-s390/pgtable.h	2007-05-22 15:20:16.000000000 +1000
@@ -744,7 +744,12 @@ ptep_establish(struct vm_area_struct *vm
 }
 
 #define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
-	ptep_establish(__vma, __address, __ptep, __entry)
+({									  \
+	int __changed = !pte_same(*(__ptep), __entry);			  \
+	if (__changed)							  \
+		ptep_establish(__vma, __address, __ptep, __entry);	  \
+	__changed;							  \
+})
 
 /*
  * Test and clear dirty bit in storage key.
Index: linux-work/include/asm-sparc/pgtable.h
===================================================================
--- linux-work.orig/include/asm-sparc/pgtable.h	2007-05-22 15:30:48.000000000 +1000
+++ linux-work/include/asm-sparc/pgtable.h	2007-05-22 15:35:56.000000000 +1000
@@ -446,6 +446,17 @@ extern int io_remap_pfn_range(struct vm_
 #define GET_IOSPACE(pfn)		(pfn >> (BITS_PER_LONG - 4))
 #define GET_PFN(pfn)			(pfn & 0x0fffffffUL)
 
+#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
+#define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
+({									  \
+	int __changed = !pte_same(*(__ptep), __entry);			  \
+	if (__changed) {						  \
+		set_pte_at((__vma)->vm_mm, (__address), __ptep, __entry); \
+		flush_tlb_page(__vma, __address);			  \
+	}								  \
+	(sparc_cpu_model == sun4c) || __changed;			  \
+})
+
 #include <asm-generic/pgtable.h>
 
 #endif /* !(__ASSEMBLY__) */
Index: linux-work/include/asm-x86_64/pgtable.h
===================================================================
--- linux-work.orig/include/asm-x86_64/pgtable.h	2007-05-22 15:20:40.000000000 +1000
+++ linux-work/include/asm-x86_64/pgtable.h	2007-05-22 15:21:52.000000000 +1000
@@ -395,12 +395,14 @@ static inline pte_t pte_modify(pte_t pte
  * bit at the same time. */
 #define  __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
 #define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
-	do {								  \
-		if (__dirty) {						  \
-			set_pte(__ptep, __entry);			  \
-			flush_tlb_page(__vma, __address);		  \
-		}							  \
-	} while (0)
+({									  \
+	int __changed = !pte_same(*(__ptep), __entry);			  \
+	if (__changed && __dirty) {					  \
+		set_pte(__ptep, __entry);			  	  \
+		flush_tlb_page(__vma, __address);		  	  \
+	}								  \
+	__changed;							  \
+})
 
 /* Encode and de-code a swap entry */
 #define __swp_type(x)			(((x).val >> 1) & 0x3f)