linux-kernel - Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect

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Message-ID: <CAHk-=wg-Y+svNy3CDkJjj0X_CJkSbpERLg64-Vqwq5u7SC4z0g@mail.gmail.com>
Date:   Mon, 21 Dec 2020 12:26:22 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Yu Zhao <yuzhao@...gle.com>, Peter Xu <peterx@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        linux-mm <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Pavel Emelyanov <xemul@...nvz.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        stable <stable@...r.kernel.org>,
        Minchan Kim <minchan@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect

On Mon, Dec 21, 2020 at 12:23 PM Nadav Amit <nadav.amit@...il.com> wrote:
>
> Using mmap_write_lock() was my initial fix and there was a strong pushback
> on this approach due to its potential impact on performance.

>From whom?

Somebody who doesn't understand that correctness is more important
than performance? And that userfaultfd is not the most important part
of the system?

The fact is, userfaultfd is CLEARLY BUGGY.

          Linus