linux-kernel - Re: [PATCH 0/2] page_count can't be used to decide when wp_page

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Message-ID: <X/eDBbaq7kUvGUyj@redhat.com>
Date:   Thu, 7 Jan 2021 16:54:13 -0500
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Yu Zhao <yuzhao@...gle.com>, Andy Lutomirski <luto@...nel.org>,
        Peter Xu <peterx@...hat.com>,
        Pavel Emelyanov <xemul@...nvz.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Minchan Kim <minchan@...nel.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        John Hubbard <jhubbard@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>, Jan Kara <jack@...e.cz>,
        Kirill Tkhai <ktkhai@...tuozzo.com>
Subject: Re: [PATCH 0/2] page_count can't be used to decide when wp_page_copy

On Thu, Jan 07, 2021 at 12:32:09PM -0800, Linus Torvalds wrote:
> I think Andrea is blinded by his own love for UFFDIO: when I do a
> debian codesearch for UFFDIO_WRITEPROTECT, all it finds is the kernel
> and strace (and the qemu copies of the kernel headers).

For the record, I feel obliged to reiterate I'm thinking purely in
clear_refs terms here.

It'd be great if we can only focus on clear_refs_write and nothing
else.

Like I said earlier, whatever way clear_refs/softdirty copes with
do_wp_page, uffd-wp can do the identical thing so, uffd-wp is
effectively irrelevant in this whole discussion. Clear-refs/softdirty
predates uffd-wp by several years too.

Thanks,
Andrea