Re: [PATCH v2 2/9] mm/hugetlb: separate path for hwpoison entry in copy_hugetlb_page_range()

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

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@nec.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@nec.com>
> > Cc: <stable@vger.kernel.org> # 5.18
> 
> This makes sense to me. Thanks for fixing this.
> 
> Reviewed-by: Miaohe Lin <linmiaohe@huawei.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);
> >  
> >