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Date:   Thu, 7 Jan 2021 16:25:25 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Andrea Arcangeli <aarcange@redhat.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Yu Zhao <yuzhao@google.com>, Andy Lutomirski <luto@kernel.org>,
        Peter Xu <peterx@redhat.com>,
        Pavel Emelyanov <xemul@openvz.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Minchan Kim <minchan@kernel.org>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Leon Romanovsky <leonro@nvidia.com>, Jan Kara <jack@suse.cz>,
        Kirill Tkhai <ktkhai@virtuozzo.com>
Subject: Re: [PATCH 0/2] page_count can't be used to decide when wp_page_copy
Message-ID: <20210107202525.GD504133@ziepe.ca>
References: <B1B85771-B211-4FCC-AEEF-BDFD37332C25@vmware.com>
 <20210107200402.31095-1-aarcange@redhat.com>
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On Thu, Jan 07, 2021 at 03:04:00PM -0500, Andrea Arcangeli wrote:

> vmsplice syscall API is insecure allowing long term GUP PINs without
> privilege.

Lots of places are relying on pin_user_pages long term pins of memory,
and cannot be converted to notifiers.

I don't think it is reasonable to just declare that insecure and
requires privileges, it is a huge ABI break.

FWIW, vhost tries to use notifiers as a replacement for GUP, and I
think it ended up quite strange and complicated. It is hard to
maintain performance when every access to the pages needs to hold some
protection against parallel invalidation.

Jason