Keir Fraser wrote:
We cannot use pte_clear() unless we redefine it for PAE. Currently it
reduces to set_pte() which explicitly uses the wrong ordering (sets
high *then* low, because it's normally used to introduce a mapping).
Yes, that means pte_clear() has the same bug. Why don't we redefine
pte_clear for PAE? Then the ifdef can go away.
Also, I think wmb() should be used in PAE's set_pte(), rather than the
current smp_wmb(). They reduce to the same thing, but wmb() makes it
clear this is is not an issue specific to SMP systems.
I agree with that. The problem is not related to SMP at all. I would
propose this approach.
Proposed fix for ptep_get_and_clear_full PAE bug. Pte_clear had the same
bug, so use the same fix for both.
Signed-off-by: Zachary Amsden <[email protected]>
Index: linux-2.6.17-rc/include/asm-i386/pgtable.h
===================================================================
--- linux-2.6.17-rc.orig/include/asm-i386/pgtable.h 2006-04-25 15:41:06.000000000 -0700
+++ linux-2.6.17-rc/include/asm-i386/pgtable.h 2006-04-26 08:39:42.000000000 -0700
@@ -204,7 +204,6 @@ extern unsigned long long __PAGE_KERNEL,
extern unsigned long pg0[];
#define pte_present(x) ((x).pte_low & (_PAGE_PRESENT | _PAGE_PROTNONE))
-#define pte_clear(mm,addr,xp) do { set_pte_at(mm, addr, xp, __pte(0)); } while (0)
/* To avoid harmful races, pmd_none(x) should check only the lower when PAE */
#define pmd_none(x) (!(unsigned long)pmd_val(x))
@@ -268,7 +267,7 @@ static inline pte_t ptep_get_and_clear_f
pte_t pte;
if (full) {
pte = *ptep;
- *ptep = __pte(0);
+ pte_clear(mm, addr, ptep);
} else {
pte = ptep_get_and_clear(mm, addr, ptep);
}
Index: linux-2.6.17-rc/include/asm-i386/pgtable-3level.h
===================================================================
--- linux-2.6.17-rc.orig/include/asm-i386/pgtable-3level.h 2006-04-25 15:41:06.000000000 -0700
+++ linux-2.6.17-rc/include/asm-i386/pgtable-3level.h 2006-04-26 08:38:57.000000000 -0700
@@ -85,6 +85,13 @@ static inline void pud_clear (pud_t * pu
#define pmd_offset(pud, address) ((pmd_t *) pud_page(*(pud)) + \
pmd_index(address))
+static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
+{
+ ptep->pte_low = 0;
+ wmb();
+ ptep->pte_high = 0;
+}
+
static inline pte_t ptep_get_and_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
{
pte_t res;
Index: linux-2.6.17-rc/include/asm-i386/pgtable-2level.h
===================================================================
--- linux-2.6.17-rc.orig/include/asm-i386/pgtable-2level.h 2006-04-25 15:41:06.000000000 -0700
+++ linux-2.6.17-rc/include/asm-i386/pgtable-2level.h 2006-04-26 08:37:34.000000000 -0700
@@ -18,6 +18,8 @@
#define set_pte_atomic(pteptr, pteval) set_pte(pteptr,pteval)
#define set_pmd(pmdptr, pmdval) (*(pmdptr) = (pmdval))
+#define pte_clear(mm,addr,xp) do { set_pte_at(mm, addr, xp, __pte(0)); } while (0)
+
#define ptep_get_and_clear(mm,addr,xp) __pte(xchg(&(xp)->pte_low, 0))
#define pte_same(a, b) ((a).pte_low == (b).pte_low)
#define pte_page(x) pfn_to_page(pte_pfn(x))
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