linux-kernel - Re: [PATCH 03/17] pci: Only allow WC mmap on prefetchable resources

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: <CAK8P3a2R_EXSp4bmBWDmyCYnaW1rOjsTUjwGwg1eEJ4psAb7sw@mail.gmail.com>
Date:   Fri, 24 Mar 2017 17:05:48 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     linux-pci <linux-pci@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/17] pci: Only allow WC mmap on prefetchable resources

On Wed, Mar 22, 2017 at 2:25 PM, David Woodhouse <dwmw2@...radead.org> wrote:
> From: David Woodhouse <dwmw@...zon.co.uk>
>
> The /proc/bus/pci mmap interface allows the user to specify whether they
> want WC or not. Don't let them do so on non-prefetchable BARs.
>
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Cc: stable@...r.kernel.org

Can you explain this a little more? I understand that we usually want to use
WC mappings on prefetchable BARs, and uncached non-WC on
non-prefetchable, but why do we have to force an error here?

Couldn't there be some hardware that allows write-combining access
but no prefetches?

       Arnd