Re: [PATCH] ppc64: Fix possible race with set_pte on a present PTE

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

Ok, here it is. I blasted ptep_establish completely and the macro
thing and changed the function to ptep_set_access_flags() which
becomes also responsible for the flush if necesary.

Overall, I feel it's more consistent this way with the other stuff
in there.

I did the ppc64 impl, the x86 one (hope I got it right). I still need to
do ppc32 and I suppose s390 must be fixed now that ptep_estabish is gone
but I'll leave that to someone who understand something about these things ;)

Here it is, boots on g5 :

===== include/asm-generic/pgtable.h 1.5 vs edited =====
--- 1.5/include/asm-generic/pgtable.h	2004-05-26 06:04:54 +10:00
+++ edited/include/asm-generic/pgtable.h	2004-05-26 15:37:02 +10:00
@@ -1,24 +1,11 @@
 #ifndef _ASM_GENERIC_PGTABLE_H
 #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
- */
-#define ptep_establish(__vma, __address, __ptep, __entry, __dirty)	\
-do {									\
-	ptep_update_dirty_accessed(__ptep, __entry, __dirty);		\
-	flush_tlb_page(__vma, __address);				\
+#ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
+#define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
+do {				  					  \
+	set_pte(__ptep, __entry);					  \
+	flush_tlb_page(__vma, __address);				  \
 } while (0)
 #endif
 
===== include/asm-i386/pgtable.h 1.45 vs edited =====
--- 1.45/include/asm-i386/pgtable.h	2004-05-26 06:04:54 +10:00
+++ edited/include/asm-i386/pgtable.h	2004-05-26 15:34:57 +10:00
@@ -325,9 +325,13 @@
  * bit at the same time.
  */
 #define update_mmu_cache(vma,address,pte) do { } while (0)
-#define ptep_update_dirty_accessed(__ptep, __entry, __dirty)	\
-	do {							\
-		if (__dirty) set_pte(__ptep, __entry);		\
+#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)
 
 /* Encode and de-code a swap entry */
===== include/asm-ppc64/pgtable.h 1.33 vs edited =====
--- 1.33/include/asm-ppc64/pgtable.h	2004-05-23 07:56:24 +10:00
+++ edited/include/asm-ppc64/pgtable.h	2004-05-26 15:32:38 +10:00
@@ -306,7 +306,10 @@
 	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 @@
 	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;
 }
@@ -396,10 +399,34 @@
  */
 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 tmp;
+
+	__asm__ __volatile__(
+	       "1:     ldarx   %0,0,%3\n\
+                or      %0,%2,%0\n\
+                stdcx.  %0,0,%3\n\
+                bne-    1b"
+	:"=&r" (tmp), "=m" (*ptep)
+	:"r" (bits), "r" (ptep)
+	:"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".
===== mm/memory.c 1.177 vs edited =====
--- 1.177/mm/memory.c	2004-05-26 05:37:09 +10:00
+++ edited/mm/memory.c	2004-05-26 15:35:40 +10:00
@@ -1004,7 +1004,11 @@
 	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);
+
+	/* Get rid of the old entry, replace with new */
+	ptep_clear_flush(vma, address, page_table);
+	set_pte(page_table, entry);
+
 	update_mmu_cache(vma, address, entry);
 }
 
@@ -1056,7 +1060,7 @@
 			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 +1650,7 @@
 		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);


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