Messages in this thread Patch in this message | | | Date | Wed, 26 Apr 2006 16:57:53 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: [PATCH] i386: PAE entries must have their low word cleared first |
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On Wed, 26 Apr 2006, Zachary Amsden wrote: > 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.
Good, we agree.
> > 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.
Attachment included...
> Proposed fix for ptep_get_and_clear_full PAE bug. Pte_clear had the same > bug, so use the same fix for both.
You need to expand that comment with text from Jan & Keir's patch: Andrew will want to know just what this bug was. The patch looks good to me, except for the unnecessary do { } while (0) in the definition of pte_clear: ah, you're only copying what was already there, can't blame you for that, let's not worry about it.
Hugh
> 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)) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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