linux-kernel - Re: [PATCH 1/2] mm: introduce put_user

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAPcyv4ii1F3iRv7TnnT2QAG+M4fst7Cu=8zggVauSizEmCtfTw@mail.gmail.com>
Date:   Tue, 4 Dec 2018 17:00:17 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     John Hubbard <john.hubbard@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>, Jan Kara <jack@...e.cz>,
        tom@...pey.com, Al Viro <viro@...iv.linux.org.uk>, benve@...co.com,
        Christoph Hellwig <hch@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        "Dalessandro, Dennis" <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jérôme Glisse <jglisse@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>, mike.marciniszyn@...el.com,
        rcampbell@...dia.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions

On Tue, Dec 4, 2018 at 4:58 PM John Hubbard <jhubbard@...dia.com> wrote:
>
> On 12/4/18 3:03 PM, Dan Williams wrote:
> > On Tue, Dec 4, 2018 at 1:56 PM John Hubbard <jhubbard@...dia.com> wrote:
[..]
> > Ok, sorry, I mis-remembered. So, you're effectively trying to capture
> > the end of the page pin event separate from the final 'put' of the
> > page? Makes sense.
> >
>
> Yes, that's it exactly.
>
> >> I was not able to actually find any place where a single additional page
> >> bit would help our situation, which is why this still uses LRU fields for
> >> both the two bits required (the RFC [1] still applies), and the dma_pinned_count.
> >
> > Except the LRU fields are already in use for ZONE_DEVICE pages... how
> > does this proposal interact with those?
>
> Very badly: page->pgmap and page->hmm_data both get corrupted. Is there an entire
> use case I'm missing: calling get_user_pages() on ZONE_DEVICE pages? Said another
> way: is it reasonable to disallow calling get_user_pages() on ZONE_DEVICE pages?
>
> If we have to support get_user_pages() on ZONE_DEVICE pages, then the whole
> LRU field approach is unusable.

Unfortunately, the entire motivation for ZONE_DEVICE was to support
get_user_pages() for persistent memory.