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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 17 Dec 2021 12:45:45 -0800
Message-ID: <CAHk-=wir5fG_OGe_38nhJZegw0uL5+0oH3k48xWQLcAwc4W0Rg@mail.gmail.com>
Subject: Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via
 FAULT_FLAG_UNSHARE (!hugetlb)
To:     David Hildenbrand <david@redhat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        David Rientjes <rientjes@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Yang Shi <shy828301@gmail.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
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On Fri, Dec 17, 2021 at 12:42 PM David Hildenbrand <david@redhat.com> wrote:
>
> > Then somebody else modified that page, and you got exactly what you
> > asked for - a COW event. The original R/O pin has the original page
> > that it asked for, and can read it just fine.
>
> Where in the code did I ask for a COW event? I asked for a R/O pin, not
> any kind of memory protection.

Why didn't you ask for a shared pin, if that is what you want?

We already support that.

If you don't like the read-only pins, don't use them. It's that simple.

              Linus