Messages in this thread Patch in this message | | | Date | Wed, 26 Apr 2006 08:44:26 -0700 | From | Zachary Amsden <> | Subject | Re: [PATCH] i386: PAE entries must have their low word cleared first |
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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 <zach@vmware.com>
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)) | |