From 86df86424939d316b1f6cfac1b6204f0c7dee317 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Tue, 8 Jul 2008 15:58:16 +1000 Subject: [PATCH] Correct hash flushing from huge_ptep_set_wrprotect() As Andy Whitcroft recently pointed out, the current powerpc version of huge_ptep_set_wrprotect() has a bug. It just calls ptep_set_wrprotect() which in turn calls pte_update() then hpte_need_flush() with the 'huge' argument set to 0. This will cause hpte_need_flush() to flush the wrong hash entries (of any). Andy's fix for this is already in the powerpc tree as commit 016b33c4958681c24056abed8ec95844a0da80a3. I have confirmed this is a real bug, not masked by some other synchronization, with a new testcase for libhugetlbfs. A process write a (MAP_PRIVATE) hugepage mapping, fork(), then alter the mapping and have the child incorrectly see the second write. Therefore, this should be fixed for 2.6.26, and for the stable tree. Here is a suitable patch for 2.6.26, which I think will also be suitable for the stable tree (neither of the headers in question has been changed much recently). It is cut down slighlty from Andy's original version, in that it does not include a 32-bit version of huge_ptep_set_wrprotect(). Currently, hugepages are not supported on any 32-bit powerpc platform. When they are, a suitable 32-bit version can be added - the only 32-bit hardware which supports hugepages does not use the conventional hashtable MMU and so will have different needs anyway. Signed-off-by: Andy Whitcroft Signed-off-by: David Gibson Signed-off-by: Benjamin Herrenschmidt Signed-off-by: Linus Torvalds --- include/asm-powerpc/hugetlb.h | 6 ------ include/asm-powerpc/pgtable-ppc64.h | 10 ++++++++++ 2 files changed, 10 insertions(+), 6 deletions(-) diff --git a/include/asm-powerpc/hugetlb.h b/include/asm-powerpc/hugetlb.h index 649c6c3b87b3..be32ff02f4a0 100644 --- a/include/asm-powerpc/hugetlb.h +++ b/include/asm-powerpc/hugetlb.h @@ -49,12 +49,6 @@ static inline pte_t huge_pte_wrprotect(pte_t pte) return pte_wrprotect(pte); } -static inline void huge_ptep_set_wrprotect(struct mm_struct *mm, - unsigned long addr, pte_t *ptep) -{ - ptep_set_wrprotect(mm, addr, ptep); -} - static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep, pte_t pte, int dirty) diff --git a/include/asm-powerpc/pgtable-ppc64.h b/include/asm-powerpc/pgtable-ppc64.h index cc6a43ba41d0..7686569a0bef 100644 --- a/include/asm-powerpc/pgtable-ppc64.h +++ b/include/asm-powerpc/pgtable-ppc64.h @@ -314,6 +314,16 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr, old = pte_update(mm, addr, ptep, _PAGE_RW, 0); } +static inline void huge_ptep_set_wrprotect(struct mm_struct *mm, + unsigned long addr, pte_t *ptep) +{ + unsigned long old; + + if ((pte_val(*ptep) & _PAGE_RW) == 0) + return; + old = pte_update(mm, addr, ptep, _PAGE_RW, 1); +} + /* * We currently remove entries from the hashtable regardless of whether * the entry was young or dirty. The generic routines only flush if the