Re: [PATCH 3.12 100/170] hugetlb: fix copy_hugetlb_page_range() to handle migration/hwpoisoned entry

Hugh Dickins
2014-07-18T18:54:53Z

On Fri, 18 Jul 2014, Jiri Slaby wrote:

> From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>
> 3.12-stable review patch. If anyone has any objections, please let me know.
>
> ===============
>
> commit 4a705fef986231a3e7a6b1a6d3c37025f021f49f upstream.
>
> There's a race between fork() and hugepage migration, as a result we try
> to "dereference" a swap entry as a normal pte, causing kernel panic.
> The cause of the problem is that copy_hugetlb_page_range() can't handle
> "swap entry" family (migration entry and hwpoisoned entry) so let's fix
> it.
>
> [akpm@linux-foundation.org: coding-style fixes]
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Acked-by: Hugh Dickins <hughd@google.com>
> Cc: Christoph Lameter <cl@linux.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>

Please drop this one for now: other -stables have carried it, but it
was found yesterday to contain a bug of its own, arguably worse than
what it's fixing. Naoya-san has done the fix for that, it's in mmotm
and should make its way to Linus probably next week: so please hold
this back until that can join it - thanks.

Hugh

> ---
> mm/hugetlb.c | 71 ++++++++++++++++++++++++++++++++++++------------------------
> 1 file changed, 43 insertions(+), 28 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 92e103b72dcb..11c2b7fed052 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2381,6 +2381,31 @@ static void set_huge_ptep_writable(struct vm_area_struct *vma,
> update_mmu_cache(vma, address, ptep);
> }
>
> +static int is_hugetlb_entry_migration(pte_t pte)
> +{
> + swp_entry_t swp;
> +
> + if (huge_pte_none(pte) || pte_present(pte))
> + return 0;
> + swp = pte_to_swp_entry(pte);
> + if (non_swap_entry(swp) && is_migration_entry(swp))
> + return 1;
> + else
> + return 0;
> +}
> +
> +static int is_hugetlb_entry_hwpoisoned(pte_t pte)
> +{
> + swp_entry_t swp;
> +
> + if (huge_pte_none(pte) || pte_present(pte))
> + return 0;
> + swp = pte_to_swp_entry(pte);
> + if (non_swap_entry(swp) && is_hwpoison_entry(swp))
> + return 1;
> + else
> + return 0;
> +}
>
> int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
> struct vm_area_struct *vma)
> @@ -2408,10 +2433,26 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
>
> spin_lock(&dst->page_table_lock);
> spin_lock_nested(&src->page_table_lock, SINGLE_DEPTH_NESTING);
> - if (!huge_pte_none(huge_ptep_get(src_pte))) {
> + entry = huge_ptep_get(src_pte);
> + if (huge_pte_none(entry)) { /* skip none entry */
> + ;
> + } else if (unlikely(is_hugetlb_entry_migration(entry) ||
> + is_hugetlb_entry_hwpoisoned(entry))) {
> + swp_entry_t swp_entry = pte_to_swp_entry(entry);
> +
> + if (is_write_migration_entry(swp_entry) && cow) {
> + /*
> + * COW mappings require pages in both
> + * parent and child to be set to read.
> + */
> + make_migration_entry_read(&swp_entry);
> + entry = swp_entry_to_pte(swp_entry);
> + set_huge_pte_at(src, addr, src_pte, entry);
> + }
> + set_huge_pte_at(dst, addr, dst_pte, entry);
> + } else {
> if (cow)
> huge_ptep_set_wrprotect(src, addr, src_pte);
> - entry = huge_ptep_get(src_pte);
> ptepage = pte_page(entry);
> get_page(ptepage);
> page_dup_rmap(ptepage);
> @@ -2426,32 +2467,6 @@ nomem:
> return -ENOMEM;
> }
>
> -static int is_hugetlb_entry_migration(pte_t pte)
> -{
> - swp_entry_t swp;
> -
> - if (huge_pte_none(pte) || pte_present(pte))
> - return 0;
> - swp = pte_to_swp_entry(pte);
> - if (non_swap_entry(swp) && is_migration_entry(swp))
> - return 1;
> - else
> - return 0;
> -}
> -
> -static int is_hugetlb_entry_hwpoisoned(pte_t pte)
> -{
> - swp_entry_t swp;
> -
> - if (huge_pte_none(pte) || pte_present(pte))
> - return 0;
> - swp = pte_to_swp_entry(pte);
> - if (non_swap_entry(swp) && is_hwpoison_entry(swp))
> - return 1;
> - else
> - return 0;
> -}
> -
> void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
> unsigned long start, unsigned long end,
> struct page *ref_page)
> --
> 2.0.0