linux-kernel - Re: [PATCH 1/3] mm/hugetlb: Pre-allocate pgtable pages for uffd wr-protects

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Message-ID: <CADrL8HW0cJn+kuPp5CD1ponepDsBpyfDQEDP3cYjdxcK6uC5Rw@mail.gmail.com>
Date:   Thu, 5 Jan 2023 01:50:42 +0000
From:   James Houghton <jthoughton@...gle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-stable <stable@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm/hugetlb: Pre-allocate pgtable pages for uffd wr-protects

On Wed, Jan 4, 2023 at 10:52 PM Peter Xu <peterx@...hat.com> wrote:
>
> Userfaultfd-wp uses pte markers to mark wr-protected pages for both shmem
> and hugetlb.  Shmem has pre-allocation ready for markers, but hugetlb path
> was overlooked.
>
> Doing so by calling huge_pte_alloc() if the initial pgtable walk fails to
> find the huge ptep.  It's possible that huge_pte_alloc() can fail with high
> memory pressure, in that case stop the loop immediately and fail silently.
> This is not the most ideal solution but it matches with what we do with
> shmem meanwhile it avoids the splat in dmesg.
>
> Cc: linux-stable <stable@...r.kernel.org> # 5.19+
> Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes")
> Reported-by: James Houghton <jthoughton@...gle.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  mm/hugetlb.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)

Acked-by: James Houghton <jthoughton@...gle.com>