The quilt patch titled
Subject: mm/hugetlb: make detecting shared pte more reliable
has been removed from the -mm tree. Its filename was
mm-hugetlb-make-detecting-shared-pte-more-reliable.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Subject: mm/hugetlb: make detecting shared pte more reliable
Date: Tue, 16 Aug 2022 21:05:53 +0800
If the pagetables are shared, we shouldn't copy or take references. Since
src could have unshared and dst shares with another vma, huge_pte_none()
is thus used to determine whether dst_pte is shared. But this check isn't
reliable. A shared pte could have pte none in pagetable in fact. The
page count of ptep page should be checked here in order to reliably
determine whether pte is shared.
[lukas.bulwahn@xxxxxxxxx: remove unused local variable dst_entry in copy_hugetlb_page_range()]
Link: https://lkml.kernel.org/r/20220822082525.26071-1-lukas.bulwahn@xxxxxxxxx
Link: https://lkml.kernel.org/r/20220816130553.31406-7-linmiaohe@xxxxxxxxxx
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 21 ++++++++-------------
1 file changed, 8 insertions(+), 13 deletions(-)
--- a/mm/hugetlb.c~mm-hugetlb-make-detecting-shared-pte-more-reliable
+++ a/mm/hugetlb.c
@@ -4750,7 +4750,7 @@ int copy_hugetlb_page_range(struct mm_st
struct vm_area_struct *dst_vma,
struct vm_area_struct *src_vma)
{
- pte_t *src_pte, *dst_pte, entry, dst_entry;
+ pte_t *src_pte, *dst_pte, entry;
struct page *ptepage;
unsigned long addr;
bool cow = is_cow_mapping(src_vma->vm_flags);
@@ -4795,15 +4795,13 @@ int copy_hugetlb_page_range(struct mm_st
/*
* If the pagetables are shared don't copy or take references.
- * dst_pte == src_pte is the common case of src/dest sharing.
*
+ * dst_pte == src_pte is the common case of src/dest sharing.
* However, src could have 'unshared' and dst shares with
- * another vma. If dst_pte !none, this implies sharing.
- * Check here before taking page table lock, and once again
- * after taking the lock below.
+ * another vma. So page_count of ptep page is checked instead
+ * to reliably determine whether pte is shared.
*/
- dst_entry = huge_ptep_get(dst_pte);
- if ((dst_pte == src_pte) || !huge_pte_none(dst_entry)) {
+ if (page_count(virt_to_page(dst_pte)) > 1) {
addr |= last_addr_mask;
continue;
}
@@ -4812,13 +4810,10 @@ int copy_hugetlb_page_range(struct mm_st
src_ptl = huge_pte_lockptr(h, src, src_pte);
spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
entry = huge_ptep_get(src_pte);
- dst_entry = huge_ptep_get(dst_pte);
again:
- if (huge_pte_none(entry) || !huge_pte_none(dst_entry)) {
+ if (huge_pte_none(entry)) {
/*
- * Skip if src entry none. Also, skip in the
- * unlikely case dst entry !none as this implies
- * sharing with another vma.
+ * Skip if src entry none.
*/
;
} else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) {
@@ -4897,7 +4892,7 @@ again:
restore_reserve_on_error(h, dst_vma, addr,
new);
put_page(new);
- /* dst_entry won't change as in child */
+ /* huge_ptep of dst_pte won't change as in child */
goto again;
}
hugetlb_install_page(dst_vma, dst_pte, addr, new);
_
Patches currently in -mm which might be from linmiaohe@xxxxxxxxxx are
mm-hwpoison-use-clearpagehwpoison-in-memory_failure.patch
mm-hwpoison-use-__pagemovable-to-detect-non-lru-movable-pages.patch
mm-hwpoison-use-num_poisoned_pages_sub-to-decrease-num_poisoned_pages.patch
mm-hwpoison-avoid-unneeded-page_mapped_in_vma-overhead-in-collect_procs_anon.patch
mm-hwpoison-check-pagetable-explicitly-in-hwpoison_user_mappings.patch
mm-hwpoison-cleanup-some-obsolete-comments.patch
writeback-remove-unused-macro-dirty_full_scope.patch
