linux-kernel - Re: [External] [PATCH] userfaultfd: hugetlbfs: fix new flag usage in error path

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Message-ID: <CAMZfGtVnGMu9SU8U+aXp6YKz0p1pBxcYy4OMpNftpkxTbJBM8w@mail.gmail.com>
Date:   Sun, 23 May 2021 10:45:11 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux- stable <stable@...r.kernel.org>
Subject: Re: [External] [PATCH] userfaultfd: hugetlbfs: fix new flag usage in
 error path

On Sat, May 22, 2021 at 7:40 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>
> In commit d6995da31122 ("hugetlb: use page.private for hugetlb specific
> page flags") the use of PagePrivate to indicate a reservation count
> should be restored at free time was changed to the hugetlb specific flag
> HPageRestoreReserve.  Changes to a userfaultfd error path as well as a
> VM_BUG_ON() in remove_inode_hugepages() were overlooked.
>
> Users could see incorrect hugetlb reserve counts if they experience an
> error with a UFFDIO_COPY operation.  Specifically, this would be the
> result of an unlikely copy_huge_page_from_user error.  There is not an
> increased chance of hitting the VM_BUG_ON.
>
> Fixes: d6995da31122 ("hugetlb: use page.private for hugetlb specific page flags")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

Reviewed-by: Muchun Song <songmuchun@...edance.com>

Thanks Mike.