linux-kernel - Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL

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: <Y8/0CaBzL0VPyE2D@nvidia.com>
Date:   Tue, 24 Jan 2023 11:06:49 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     David Howells <dhowells@...hat.com>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        linux-mm@...ck.org
Subject: Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL_GET down

On Tue, Jan 24, 2023 at 02:59:25PM +0000, David Howells wrote:
> Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > What is the 3rd state?
> 
> Consider a network filesystem message generated for a direct I/O that the
> network filesystem does zerocopy on.  You may have an sk_buff that has
> fragments from one or more of three different sources:
> 
>  (1) Fragments consisting of specifically allocated pages, such as the
>      IP/UDP/TCP headers that have refs taken on them.
> 
>  (2) Fragments consisting of zerocopy kernel buffers that has neither refs nor
>      pins belonging to the sk_buff.
> 
>      iov_iter_extract_pages() will not take pins when extracting from, say, an
>      XARRAY-type or KVEC-type iterator.  iov_iter_extract_mode() will return
>      0.
> 
>  (3) Fragments consisting of zerocopy user buffers that have pins taken on
>      them belonging to the sk_buff.
> 
>      iov_iter_extract_pages() will take pins when extracting from, say, a
>      UBUF-type or IOVEC-type iterator.  iov_iter_extract_mode() will return
>      FOLL_PIN (at the moment).
> 
> So you have three states: Ref'd, pinned and no-retention.

Isn't that this:

if (cleanup_flags & PAGE_CLEANUP_NEEDED)
   gup_put_folio(folio, 1, cleanup_flags & PAGE_CLEANUP_UNPIN)


?

Three states - decr get, decr pinned, do nothing?

Jason