linux-kernel - Re: [PATCH v4 1/1] mm: introduce put_user

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Date:   Wed, 20 Mar 2019 12:40:29 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Jerome Glisse <jglisse@...hat.com>, john.hubbard@...il.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Benvenuti <benve@...co.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Tom Talpey <tom@...pey.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4 1/1] mm: introduce put_user_page*(), placeholder
 versions

On Tue, Mar 19, 2019 at 12:24:00PM -0700, John Hubbard wrote:
> So, I could be persuaded either way. But given the lack of an visible perf
> effects, and given that this could will get removed anyway because we'll
> likely end up with set_page_dirty() called at GUP time instead...it seems
> like it's probably OK to just leave it as is.

Apart from ugly code generated, other argument might be Spectre-like
attacks on these call. I would rather avoid indirect function calls
whenever possible. And I don't think opencodded versions of these
functions would look much worse.

-- 
 Kirill A. Shutemov