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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 3 Jun 2021 12:15:39 -0700
Message-ID: <CAHk-=wg_r837DdEepGAA+jCz27Oqc5hxgYEJo9OoWrnKRhfz5g@mail.gmail.com>
Subject: Re: [PATCH 2/2] mm: adds NOSIGBUS extension for out-of-band shmem read
To:     Hugh Dickins <hughd@google.com>
Cc:     Ming Lin <mlin@kernel.org>, Simon Ser <contact@emersion.fr>,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>
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On Thu, Jun 3, 2021 at 12:12 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Yeah, if that's sufficient, then that original patch should just work as-is.

To clarify: it obviously needs the VM_xyz flags things, but the
VM_SHARED check in do_anonymous_page() is fine, and the whole issue
with VM_MAYWRITE is entirely moot.

MAP_PRIVATE works fine with zero pages even when writable - they get
COW'ed properly, of course.

               Linus