linux-kernel - Re: [PATCH v2 2/9] mm/hugetlb: separate path for hwpoison entry in copy_hugetlb_page

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Message-ID: <20220627060659.GB2159330@hori.linux.bs1.fc.nec.co.jp>
Date:   Mon, 27 Jun 2022 06:06:59 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Miaohe Lin <linmiaohe@...wei.com>
CC:     Naoya Horiguchi <nao.horiguchi@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Oscar Salvador <osalvador@...e.de>,
        Muchun Song <songmuchun@...edance.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2 2/9] mm/hugetlb: separate path for hwpoison entry in
 copy_hugetlb_page_range()

On Fri, Jun 24, 2022 at 05:23:41PM +0800, Miaohe Lin wrote:
> On 2022/6/24 7:51, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@....com>
> > 
> > Originally copy_hugetlb_page_range() handles migration entries and hwpoisone
> 
> s/hwpoisone/hwpoisoned/
> 
> > entries in similar manner.  But recently the related code path has more code
> > for migration entries, and when is_writable_migration_entry() was converted
> > to !is_readable_migration_entry(), hwpoison entries on source processes got
> > to be unexpectedly updated (which is legitimate for migration entries, but
> > not for hwpoison entries).  This results in unexpected serious issues like
> > kernel panic when foking processes with hwpoison entries in pmd.
> 
> s/foking/forking/

Sorry for many typos.  I somehow forgot to run spell checker.

> 
> > 
> > Separate the if branch into one for hwpoison entries and one for migration
> > entries.
> > 
> > Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive")
> > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> > Cc: <stable@...r.kernel.org> # 5.18
> 
> This makes sense to me. Thanks for fixing this.
> 
> Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

Thank you for reviewing!

- Naoya Horiguchi

> 
> > ---
> >  mm/hugetlb.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index c538278170a2..f59f43c06601 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -4784,8 +4784,13 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
> >  			 * sharing with another vma.
> >  			 */
> >  			;
> > -		} else if (unlikely(is_hugetlb_entry_migration(entry) ||
> > -				    is_hugetlb_entry_hwpoisoned(entry))) {
> > +		} else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) {
> > +			bool uffd_wp = huge_pte_uffd_wp(entry);
> > +
> > +			if (!userfaultfd_wp(dst_vma) && uffd_wp)
> > +				entry = huge_pte_clear_uffd_wp(entry);
> > +			set_huge_swap_pte_at(dst, addr, dst_pte, entry, sz);
> > +		} else if (unlikely(is_hugetlb_entry_migration(entry))) {
> >  			swp_entry_t swp_entry = pte_to_swp_entry(entry);
> >  			bool uffd_wp = huge_pte_uffd_wp(entry);
> >  
> >