linux-kernel - Re: [PATCH 1/3] ide: add "ignore

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Message-Id: <200905261423.40117.bzolnier@gmail.com>
Date:	Tue, 26 May 2009 14:23:39 +0200
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Frans Pop <elendil@...net.nl>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ide: add "ignore_hpa" module parameter

On Tuesday 26 May 2009 01:06:12 Frans Pop wrote:
> On Tuesday 26 May 2009, Alan Cox wrote:
> > > It's also not obvious (at least not to a dumb user like me) that
> > > "ignore HPA limit" is equivalent to "preserving the Host Protected
> > > Area" as the commit commit says.
> >
> > It isn't - its the exact reverse.
> 
> Right.
> 
> > Ignoring the HPA limit tells the kernel to ignore the system BIOS and
> > firmware set defaults and to stomp the whole disk regardless. On a
> > modern system thats almost always a really bad idea. Unfortunately on
> > ancient boxes with disk jumpers set to lie about the disk size (32GB
> > clipping etc) its the right thing.
> >
> > Having the same parameter in both stacks seems a good idea but really
> > we need Tejun's patch exposing the values and then to propogate the hpa
> > ignore into sysfs and trigger a revalidate of the disk if you change
> > it. Libata has all the framework for that ready just needing the final
> > bits. I don't see anything problematic in old IDE also having that
> > interface.
> 
> That also sounds as if it would better protect (or at least inform) 
> existing users who have file systems on disks where the HPA is currently 
> being ignored.
> 
> Seems to me this whole issue would also be worth an LWN (BCCed) article to 
> raise awareness, explain the issue, maybe give practical info how to test 
> whether you're affected, and maybe add some advice to distributions how 
> to handle it. Seems to me like it's something that should be mentioned in 
> distribution release notes.

Ironically, some distributions were a well aware of the problem, yet they
chose to ignore it *twice* over the last few years.

First time with the introduction of the default IDE HPA behavior of always
giving the access to the full capacity of a disk and leaving decisions about
HPA preservation/removal up to the installer & user.

Second time when said distributions switched from IDE to libata (which uses
the different default behavior as it limits the capacity to non-HPA part).

Please note that no fancy sysfs support was needed to prevent the problem:
both stacks (ide & libata) support HDIO_DRIVE_TASK ioctl which can be used
to execute commands needed to retrieve/change HPA setting.

Moreover the (much needed) work from Tejun doesn't help a tiny bit in case
of people migrating their *working* setups from IDE to libata (at least
in distro upgrade case this could have been handled by distro installer but
see above) and hitting the compatibility issue mentioned in bug #13365.

Anyway I'm putting all HPA fixes on hold as I have enough (thanks for your
feedback on patches - all points are valid and I will address them if I ever
take patches out of freezer).

Thanks.
Bart
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