diff --git a/Makefile b/Makefile index b6fa6316ef75..716cdade034d 100644 --- a/Makefile +++ b/Makefile @@ -1,6 +1,6 @@ VERSION = 3 PATCHLEVEL = 2 -SUBLEVEL = 82 +SUBLEVEL = 83 EXTRAVERSION = NAME = Saber-toothed Squirrel diff --git a/include/linux/mm.h b/include/linux/mm.h index e5ee683b0ad3..16394da01d2d 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1527,6 +1527,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address, #define FOLL_MLOCK 0x40 /* mark page as mlocked */ #define FOLL_SPLIT 0x80 /* don't return transhuge pages, split them */ #define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */ +#define FOLL_COW 0x4000 /* internal GUP flag */ typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr, void *data); diff --git a/mm/memory.c b/mm/memory.c index 675b211296fd..2917e9b2e4d4 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1427,6 +1427,24 @@ 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 @@ -1509,10 +1527,13 @@ 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))) @@ -1555,7 +1576,7 @@ split_fallthrough: unlock_page(page); } } -unlock: + pte_unmap_unlock(ptep, ptl); out: return page; @@ -1789,17 +1810,13 @@ 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(); }