diff options
| -rw-r--r-- | mm/memory.c | 41 |
1 files changed, 4 insertions, 37 deletions
diff --git a/mm/memory.c b/mm/memory.c index fcfc4ca36eba..eeae590e526a 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -806,8 +806,6 @@ copy_present_page(struct mm_struct *dst_mm, struct mm_struct *src_mm, return 1; /* - * The trick starts. - * * What we want to do is to check whether this page may * have been pinned by the parent process. If so, * instead of wrprotect the pte on both sides, we copy @@ -815,47 +813,16 @@ copy_present_page(struct mm_struct *dst_mm, struct mm_struct *src_mm, * the pinned page won't be randomly replaced in the * future. * - * To achieve this, we do the following: - * - * 1. Write-protect the pte if it's writable. This is - * to protect concurrent write fast-gup with - * FOLL_PIN, so that we'll fail the fast-gup with - * the write bit removed. - * - * 2. Check page_maybe_dma_pinned() to see whether this - * page may have been pinned. - * - * The order of these steps is important to serialize - * against the fast-gup code (gup_pte_range()) on the - * pte check and try_grab_compound_head(), so that - * we'll make sure either we'll capture that fast-gup - * so we'll copy the pinned page here, or we'll fail - * that fast-gup. - * - * NOTE! Even if we don't end up copying the page, - * we won't undo this wrprotect(), because the normal - * reference copy will need it anyway. - */ - if (pte_write(pte)) - ptep_set_wrprotect(src_mm, addr, src_pte); - - /* - * These are the "normally we can just copy by reference" - * checks. + * The page pinning checks are just "has this mm ever + * seen pinning", along with the (inexact) check of + * the page count. That might give false positives for + * for pinning, but it will work correctly. */ if (likely(!atomic_read(&src_mm->has_pinned))) return 1; if (likely(!page_maybe_dma_pinned(page))) return 1; - /* - * Uhhuh. It looks like the page might be a pinned page, - * and we actually need to copy it. Now we can set the - * source pte back to being writable. - */ - if (pte_write(pte)) - set_pte_at(src_mm, addr, src_pte, pte); - new_page = *prealloc; if (!new_page) return -EAGAIN; |