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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 11 Sep 2020 12:09:25 -0700
Message-ID: <CAHk-=wg0cqRnqT=pBFx+wk3mQVzuCxQ3ea_nYOTyaCG4Ohkk_Q@mail.gmail.com>
Subject: Re: [PATCH] mm/gup: fix gup_fast with dynamic page table folding
To:     Vasily Gorbik <gor@linux.ibm.com>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>, John Hubbard <jhubbard@nvidia.com>,
        Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
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        Dave Hansen <dave.hansen@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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On Fri, Sep 11, 2020 at 12:04 PM Vasily Gorbik <gor@linux.ibm.com> wrote:
>
> Currently to make sure that every page table entry is read just once
> gup_fast walks perform READ_ONCE and pass pXd value down to the next
> gup_pXd_range function by value e.g.:
[ ... ]

Ack, this looks sane to me.

I was going to ask how horrible it would be to convert all the other
users, but a quick grep convinced me that yeah, it's only GUP that is
this special, and we don't want to make this interface be the real one
for everything else too..

                Linus