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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 21 Dec 2020 15:33:30 -0800
Message-ID: <CAHk-=wiEp-D36h972CBHqJ-c8tR9fytg9tesZ1j_9B0ax9Ad_Q@mail.gmail.com>
Subject: Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect
To:     Yu Zhao <yuzhao@google.com>
Cc:     Peter Xu <peterx@redhat.com>, Nadav Amit <nadav.amit@gmail.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        linux-mm <linux-mm@kvack.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Pavel Emelyanov <xemul@openvz.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        stable <stable@vger.kernel.org>,
        Minchan Kim <minchan@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
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On Mon, Dec 21, 2020 at 3:12 PM Yu Zhao <yuzhao@google.com> wrote:
>
> I can't say I disagree with you but the man has made the call and I
> think we should just move on.

"The man" can always be convinced by numbers.

So if somebody comes up with an alternate patch, and explains it, and
shows that it is better - go for it.

I just think that if mprotect() can take the mmap lock for writing,
then userfaultfd sure as hell can. What odd load does people have
where userfaultfd is more important than mprotect?

So as far as the man is concerned, I think "just fix userfaultfd" is
simply the default obvious operation.

Not necessarily a final endpoint.

                 Linus