linux-kernel - Re: [PATCH 2/2] mm: soft_dirty: userfaultfd: introduce wrprotect_tlb_flush

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Message-ID: <20210108124815.GA4512@willie-the-truck>
Date:   Fri, 8 Jan 2021 12:48:16 +0000
From:   Will Deacon <will@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        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>,
        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>,
        Jason Gunthorpe <jgg@...pe.ca>, Jan Kara <jack@...e.cz>,
        Kirill Tkhai <ktkhai@...tuozzo.com>
Subject: Re: [PATCH 2/2] mm: soft_dirty: userfaultfd: introduce
 wrprotect_tlb_flush_pending

On Thu, Jan 07, 2021 at 04:25:54PM -0800, Linus Torvalds wrote:
> Please. Why is the correct patch not the attached one (apart from the
> obvious fact that I haven't tested it and maybe just screwed up
> completely - but you get the idea)?

It certainly looks simple and correct to me, although it means we're now
taking the mmap sem for write in the case where we only want to clear the
access flag, which should be fine with the thing only held for read, no?

Will