linux-kernel - Re: [PATCH 1/2] mm/uffd: Fix pte marker when fork() without fork event

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Message-ID: <eeedfdcb-2f9a-86fb-ab62-32cdfaf5d289@huawei.com>
Date:   Sat, 17 Dec 2022 10:59:06 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Peter Xu <peterx@...hat.com>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>
CC:     Andrea Arcangeli <aarcange@...hat.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Nadav Amit <nadav.amit@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Huang Ying <ying.huang@...el.com>, <stable@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm/uffd: Fix pte marker when fork() without fork
 event

On 2022/12/15 4:04, Peter Xu wrote:
> When fork(), dst_vma is not guaranteed to have VM_UFFD_WP even if src may
> have it and has pte marker installed.  The warning is improper along with
> the comment.  The right thing is to inherit the pte marker when needed, or
> keep the dst pte empty.
> 
> A vague guess is this happened by an accident when there's the prior patch
> to introduce src/dst vma into this helper during the uffd-wp feature got
> developed and I probably messed up in the rebase, since if we replace
> dst_vma with src_vma the warning & comment it all makes sense too.
> 
> Hugetlb did exactly the right here (copy_hugetlb_page_range()).  Fix the
> general path.
> 
> Reproducer:
> 
> https://github.com/xupengfe/syzkaller_logs/blob/main/221208_115556_copy_page_range/repro.c
> 
> Cc: <stable@...r.kernel.org> # 5.19+
> Fixes: c56d1b62cce8 ("mm/shmem: handle uffd-wp during fork()")
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216808
> Reported-by: Pengfei Xu <pengfei.xu@...el.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>

Looks good to me. Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

Thanks,
Miaohe Lin