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  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]
Date:   Mon, 18 Jun 2018 00:56:50 -0700
From:   Christoph Hellwig <>
Cc:     Matthew Wilcox <>,
        Michal Hocko <>,
        Christopher Lameter <>,
        Jason Gunthorpe <>,
        Dan Williams <>,
        Jan Kara <>,,
        LKML <>,
        linux-rdma <>,
        John Hubbard <>
Subject: Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*()

On Sat, Jun 16, 2018 at 06:25:10PM -0700, wrote:
> From: John Hubbard <>
> This fixes a few problems that come up when using devices (NICs, GPUs,
> for example) that want to have direct access to a chunk of system (CPU)
> memory, so that they can DMA to/from that memory. Problems [1] come up
> if that memory is backed by persistence storage; for example, an ext4
> file system. I've been working on several customer bugs that are hitting
> this, and this patchset fixes those bugs.

What happens if we do get_user_page from two different threads or even
processes on the same page?  As far as I can tell from your patch
the first one finishing the page will clear the bit and then we are
back to no protection.

Note that you can reproduce such a condition trivially using direct
I/O reads or writes.

Powered by blists - more mailing lists