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-rw-r--r--mm/memory.c67
1 files changed, 60 insertions, 7 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 19e0ae9beecb..d14b251a25a6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -999,17 +999,15 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
goto no_page_table;
ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
- if (!ptep)
- goto out;
pte = *ptep;
if (!pte_present(pte))
- goto unlock;
+ goto no_page;
if ((flags & FOLL_WRITE) && !pte_write(pte))
goto unlock;
page = vm_normal_page(vma, address, pte);
if (unlikely(!page))
- goto unlock;
+ goto bad_page;
if (flags & FOLL_GET)
get_page(page);
@@ -1024,6 +1022,15 @@ unlock:
out:
return page;
+bad_page:
+ pte_unmap_unlock(ptep, ptl);
+ return ERR_PTR(-EFAULT);
+
+no_page:
+ pte_unmap_unlock(ptep, ptl);
+ if (!pte_none(pte))
+ return page;
+ /* Fall through to ZERO_PAGE handling */
no_page_table:
/*
* When core dumping an enormous anonymous area that nobody
@@ -1038,6 +1045,26 @@ no_page_table:
return page;
}
+/* Can we do the FOLL_ANON optimization? */
+static inline int use_zero_page(struct vm_area_struct *vma)
+{
+ /*
+ * We don't want to optimize FOLL_ANON for make_pages_present()
+ * when it tries to page in a VM_LOCKED region. As to VM_SHARED,
+ * we want to get the page from the page tables to make sure
+ * that we serialize and update with any other user of that
+ * mapping.
+ */
+ if (vma->vm_flags & (VM_LOCKED | VM_SHARED))
+ return 0;
+ /*
+ * And if we have a fault or a nopfn routine, it's not an
+ * anonymous region.
+ */
+ return !vma->vm_ops ||
+ (!vma->vm_ops->fault && !vma->vm_ops->nopfn);
+}
+
int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, int len, int write, int force,
struct page **pages, struct vm_area_struct **vmas)
@@ -1112,8 +1139,7 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
foll_flags = FOLL_TOUCH;
if (pages)
foll_flags |= FOLL_GET;
- if (!write && !(vma->vm_flags & VM_LOCKED) &&
- (!vma->vm_ops || !vma->vm_ops->fault))
+ if (!write && use_zero_page(vma))
foll_flags |= FOLL_ANON;
do {
@@ -1159,6 +1185,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
cond_resched();
}
+ if (IS_ERR(page))
+ return i ? i : PTR_ERR(page);
if (pages) {
pages[i] = page;
@@ -1757,7 +1785,6 @@ gotten:
page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
if (likely(pte_same(*page_table, orig_pte))) {
if (old_page) {
- page_remove_rmap(old_page, vma);
if (!PageAnon(old_page)) {
dec_mm_counter(mm, file_rss);
inc_mm_counter(mm, anon_rss);
@@ -1779,6 +1806,32 @@ gotten:
lru_cache_add_active(new_page);
page_add_new_anon_rmap(new_page, vma, address);
+ if (old_page) {
+ /*
+ * Only after switching the pte to the new page may
+ * we remove the mapcount here. Otherwise another
+ * process may come and find the rmap count decremented
+ * before the pte is switched to the new page, and
+ * "reuse" the old page writing into it while our pte
+ * here still points into it and can be read by other
+ * threads.
+ *
+ * The critical issue is to order this
+ * page_remove_rmap with the ptp_clear_flush above.
+ * Those stores are ordered by (if nothing else,)
+ * the barrier present in the atomic_add_negative
+ * in page_remove_rmap.
+ *
+ * Then the TLB flush in ptep_clear_flush ensures that
+ * no process can access the old page before the
+ * decremented mapcount is visible. And the old page
+ * cannot be reused until after the decremented
+ * mapcount is visible. So transitively, TLBs to
+ * old page will be flushed before it can be reused.
+ */
+ page_remove_rmap(old_page, vma);
+ }
+
/* Free the old page.. */
new_page = old_page;
ret |= VM_FAULT_WRITE;