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    SubjectRe: [PATCH 3.8 107/116] hugetlb: fix copy_hugetlb_page_range() to handle migration/hwpoisoned entry
    On Tue, 22 Jul 2014, Kamal Mostafa wrote:

    > 3.8.13.27 -stable review patch. If anyone has any objections, please let me know.
    >
    > ------------------
    >
    > From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    >
    > 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: Kamal Mostafa <kamal@canonical.com>

    Please drop this one for now: other -stables have carried it, but it
    was found last week 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 this 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 35fc5eb..7b180d7 100644
    > --- a/mm/hugetlb.c
    > +++ b/mm/hugetlb.c
    > @@ -2291,6 +2291,31 @@ 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)
    > @@ -2318,10 +2343,26 @@ 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);
    > @@ -2336,32 +2377,6 @@ 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)
    > --
    > 1.9.1
    >
    > --
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