diff options
Diffstat (limited to 'mm/memory.c')
| -rw-r--r-- | mm/memory.c | 39 |
1 files changed, 28 insertions, 11 deletions
diff --git a/mm/memory.c b/mm/memory.c index 4774579d8acb..97019112eac4 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1447,6 +1447,24 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address, } EXPORT_SYMBOL_GPL(zap_vma_ptes); +static inline bool can_follow_write_pte(pte_t pte, struct page *page, + unsigned int flags) +{ + if (pte_write(pte)) + return true; + + /* + * Make sure that we are really following CoWed page. We do not really + * have to care about exclusiveness of the page because we only want + * to ensure that once COWed page hasn't disappeared in the meantime + * or it hasn't been merged to a KSM page. + */ + if ((flags & FOLL_FORCE) && (flags & FOLL_COW)) + return page && PageAnon(page) && !PageKsm(page); + + return false; +} + /** * follow_page - look up a page descriptor from a user-virtual address * @vma: vm_area_struct mapping @address @@ -1529,10 +1547,13 @@ split_fallthrough: pte = *ptep; if (!pte_present(pte)) goto no_page; - if ((flags & FOLL_WRITE) && !pte_write(pte)) - goto unlock; page = vm_normal_page(vma, address, pte); + if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, page, flags)) { + pte_unmap_unlock(ptep, ptl); + return NULL; + } + if (unlikely(!page)) { if ((flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(pte))) @@ -1575,7 +1596,7 @@ split_fallthrough: unlock_page(page); } } -unlock: + pte_unmap_unlock(ptep, ptl); out: return page; @@ -1809,17 +1830,13 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, * The VM_FAULT_WRITE bit tells us that * do_wp_page has broken COW when necessary, * even if maybe_mkwrite decided not to set - * pte_write. We can thus safely do subsequent - * page lookups as if they were reads. But only - * do so when looping for pte_write is futile: - * in some cases userspace may also be wanting - * to write to the gotten user page, which a - * read fault here might prevent (a readonly - * page might get reCOWed by userspace write). + * pte_write. We cannot simply drop FOLL_WRITE + * here because the COWed page might be gone by + * the time we do the subsequent page lookups. */ if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE)) - foll_flags &= ~FOLL_WRITE; + foll_flags |= FOLL_COW; cond_resched(); } |