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Subject[PATCH] ppc32: Fix pte_update for 64-bit PTEs

(this should probably go in for 2.6.12)

While the existing pte_update code handled atomically modifying a 64-bit
PTE, it did not return all 64-bits of the PTE before it was modified.
This causes problems in some places that expect the full PTE to be
returned, like ptep_get_and_clear().

Created a new pte_update function that is conditional on CONFIG_PTE_64BIT.
It atomically reads the low PTE word which all PTE flags are required to
be in and returns a premodified full 64-bit PTE.

Since we now have an explicit 64-bit PTE version of pte_update we can also
remove the hack that existed to get the low PTE word regardless of size.

Signed-off-by: Kumar Gala <>


diff -Nru a/include/asm-ppc/pgtable.h b/include/asm-ppc/pgtable.h
--- a/include/asm-ppc/pgtable.h 2005-04-07 14:01:09 -05:00
+++ b/include/asm-ppc/pgtable.h 2005-04-07 14:01:09 -05:00
@@ -526,10 +526,10 @@
* Atomic PTE updates.
* pte_update clears and sets bit atomically, and returns
- * the old pte value.
- * The ((unsigned long)(p+1) - 4) hack is to get to the least-significant
- * 32 bits of the PTE regardless of whether PTEs are 32 or 64 bits.
+ * the old pte value. In the 64-bit PTE case we lock around the
+ * low PTE word since we expect ALL flag bits to be there
+#ifndef CONFIG_PTE_64BIT
static inline unsigned long pte_update(pte_t *p, unsigned long clr,
unsigned long set)
@@ -543,10 +543,31 @@
" stwcx. %1,0,%3\n\
bne- 1b"
: "=&r" (old), "=&r" (tmp), "=m" (*p)
- : "r" ((unsigned long)(p+1) - 4), "r" (clr), "r" (set), "m" (*p)
+ : "r" (p), "r" (clr), "r" (set), "m" (*p)
: "cc" );
return old;
+static inline unsigned long long pte_update(pte_t *p, unsigned long clr,
+ unsigned long set)
+ unsigned long long old;
+ unsigned long tmp;
+ __asm__ __volatile__("\
+1: lwarx %L0,0,%4\n\
+ lwzx %0,0,%3\n\
+ andc %1,%L0,%5\n\
+ or %1,%1,%6\n"
+ PPC405_ERR77(0,%3)
+" stwcx. %1,0,%4\n\
+ bne- 1b"
+ : "=&r" (old), "=&r" (tmp), "=m" (*p)
+ : "r" (p), "r" ((unsigned long)(p) + 4), "r" (clr), "r" (set), "m" (*p)
+ : "cc" );
+ return old;

* set_pte stores a linux PTE into the linux page table.
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