linux-kernel - Re: [PATCH AUTOSEL for-4.9 04/53] spi: imx: adjust watermark level according to transfer length

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]

Date:   Wed, 8 Nov 2017 22:11:02 +0000
From:   Mark Brown <broonie@...nel.org>
To:     "Levin, Alexander (Sasha Levin)" <alexander.levin@....verizon.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Jiada Wang <jiada_wang@...tor.com>
Subject: Re: [PATCH AUTOSEL for-4.9 04/53] spi: imx: adjust watermark level
 according to transfer length

On Wed, Nov 08, 2017 at 09:39:11PM +0000, Levin, Alexander (Sasha Levin) wrote:
> >On Wed, Nov 08, 2017 at 08:49:55PM +0000, Levin, Alexander (Sasha Levin) wrote:
> >This seems like an optimization not a bug fix...

> Hm, is it? I read it as "DMA is not being used at all even though we
> thought we're using it".

Yes, that's how I read it too.  

> Yes, the impact is "just" performance, but doesn't it result in quite
> a significat impact?

Only about double according to the initial commit adding DMA support
which is frankly a bit disappointing although yeah, it's a big win.  My
worry is that if there's a problem with DMA on some device for which a
fix wasn't backported (or where we're using a fallback) this could
expose problems if we start using it.  If you look at the history of the
driver there's some quirks were added later on for example, and I didn't
check the DMA controller drivers or anything and obviously can't see any
out of tree code users may have.

*Probably* it doesn't break anything but since it's not fixing anything
and the risk is data corruption I'd be much more comfortable with a more
thorough risk analysis.

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)