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

Benjamin Herrenschmidt
2004-05-26T05:41:46Z

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);