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] [day] [month] [year] [list]
Date:   Wed, 4 Apr 2018 20:06:42 -0400
From:   Sinan Kaya <>
To:     Arnd Bergmann <>
Cc:     Palmer Dabbelt <>,
        Mark Rutland <>,
        Timur Tabi <>,,,
        Linux ARM <>,
        linux-arch <>,
        Linux Kernel Mailing List <>
Subject: Re: [PATCH v2 2/2] io: prevent compiler reordering on the default
 readX() implementation

On 4/4/2018 3:50 PM, Arnd Bergmann wrote:
> On Wed, Apr 4, 2018 at 7:48 PM, Sinan Kaya <> wrote:
>> On 4/4/2018 11:55 AM, Arnd Bergmann wrote:
>>> Yes, exactly, plus the same for write and in/out of course.
>> I was looking at this...
>> inb() and outb() seem to be calling writeb(). It gets the wmb/barrier automatically
>> when we fix writeb().
>> Did I miss something?
> At least outb() needs stricter barriers than writeb() in theory, what
> we want here
> is that outb() has not just made it out to the device but that the
> write has been
> confirmed completed by the device. Some architectures can't do it, but those
> that can should have an easy way to hook into that using a separate set of
> barriers.
> Using the riscv barrier names, we could do this like
> #ifndef __io_bw()
> #define __io_bw()      wmb()
> #endif
> #ifndef __io_aw
> #define __io_aw()      barrier()
> #endif
> #ifndef __io_pbw
> #define __io_pbw()     __io_bw()
> #endif
> #ifndef __io_paw
> #define __io_paw()     __io_aw()
> #endif
> and the same thing for reads. This way, an architecture could override
> any of those, but still get reasonable defaults for the others.
> For __io_bw(), I picked barrier() instead of do {} while (0), no idea
> if that's any better, I just play safe here.

I posted V3. I hope I captured what you mean above correctly.

>      Arnd

Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

Powered by blists - more mailing lists