linux-kernel - Re: [PATCH v9 03/16] iommu/exynos: fix page table maintenance

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: <CANEJEGveOtGs8XEYFnnXoZ575bqKRkc3AMikr_1x02cNikwTng@mail.gmail.com>
Date:	Wed, 14 Aug 2013 13:54:53 -0700
From:	Grant Grundler <grundler@...omium.org>
To:	Joerg Roedel <joro@...tes.org>
Cc:	Grant Grundler <grundler@...omium.org>,
	Tomasz Figa <t.figa@...sung.com>,
	Cho KyongHo <pullip.cho@...sung.com>,
	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	Linux IOMMU <iommu@...ts.linux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>,
	devicetree@...r.kernel.org, Kukjin Kim <kgene.kim@...sung.com>,
	Prathyush <prathyush.k@...sung.com>,
	Rahul Sharma <rahul.sharma@...sung.com>,
	Subash Patel <supash.ramaswamy@...aro.org>,
	Antonios Motakis <a.motakis@...tualopensystems.com>,
	kvmarm@...ts.cs.columbia.edu,
	Sachin Kamat <sachin.kamat@...aro.org>
Subject: Re: [PATCH v9 03/16] iommu/exynos: fix page table maintenance

On Wed, Aug 14, 2013 at 3:49 AM, Joerg Roedel <joro@...tes.org> wrote:
> On Thu, Aug 08, 2013 at 11:28:44AM -0700, Grant Grundler wrote:
>> I can't speak to the previous BUG_ON(). I believe the EADDRESSINUSE
>> failures could be either WARN_ON or BUG_ON.   This condition is
>> clearly a bug in the generic IOMMU allocator and I think that's why
>> KyongHo Cho used BUG_ON.
>>
>> Handing out duplicate addresses will generally lead to some sort of
>> data corruption or other fault depending on how robust the underlying
>> device drivers are written.  So my preference is a BUG_ON to
>> immediately flag this condition instead of hoping a device driver will
>> correctly handling the dma mapping failure (Some do, most currently
>> don't).
>>
>> WARN_ON() + return -EADDRESSINUSE would be a good alternative.
>
> Even if it is a real BUG condition, I don't think it is worth to stop
> execution at this point. It makes debugging harder and the system less
> reliable. I prefer to go with the WARN_ON and an error return value.

I'm ok with WARN_ON and an error return value. This is "valid"
behavior.  I expect this bug to never happen but if and when it does,
I want a clear symptom (e.g. WARN_ON) that it happened.

My concern is that historically, drivers did not get an error return
value on failure:
    ftp://193.166.3.4/pub/linux/kernel/v2.3/patch-html/patch-2.3.47/linux_Documentation_DMA-mapping.txt.html

or later:
    https://www.kernel.org/pub/linux/kernel/people/marcelo/linux-2.4/Documentation/DMA-mapping.txt

And thus, some drivers don't check or attempt to handle mapping
failures based on this existing code. Here is a recent example:
     http://comments.gmane.org/gmane.linux.network/272969

I hope very few or none of those exist since Neil Horman demonstrated
"dma debugging" can flag this behavior.

Just for fun, I'll include this link : (apperently 2003 was a good
year for DMA talks :)
     http://ols.fedoraproject.org/OLS/Reprints-2003/LinuxSymposium2003-2side.pdf
     (three talks on DMA issues)

thanks
grant
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/