Re: libata: implement on-demand HPA unlocking

[Greg Freemyer <greg.freemyer@gmail.com>]

On Wed, Feb 9, 2011 at 2:36 PM, Phillip Susi <psusi@cfl.rr.com> wrote:
> On 2/9/2011 10:37 AM, Alan Cox wrote:
>> Unlocking the HPA is actually necessary for sanity on a lot of systems
>
> Right.. ones that were partitioned using an older kernel with the buggy
> behavior of unlocking it by default.
>
>> too, and there are really no standards. Remember the primary use of HPA
>> has actually been to hide most of the disk from buggy BIOSen so that the
>> OS can then unlock it after the BIOS has stopped looking.
>
> The ATA spec describes the HPA saying:
>
> A reserved area for data storage outside the normal operating system
> file system is required for several
> specialized applications.
>
> This tells me that it is intended for the bios to reserve an area of the
> disk that the OS should NOT access.  So far the only use of it that I
> have seen is by bioses to hide a small area, presumably to store
> platform specific information.  I see about a dozen reports on the
> ubuntu forums and bug tracker each year of people with HPA problems and
> it always seems to be a small area, as opposed to hiding everything
> above 128 MB or something.
>

Philip,

At some point (maybe 10 years ago), Dell used a HPA hidden partition
to hold a diagnostic partition of some sort.  I never used it, but I
remember coming across it several times.  I don't recall how big it
was.

I assume their thought was to have a recovery / diagnostic area that
normal users couldn't get to.  Now they just use a normal partition
for that.

I gather fakeraids now use a HPA protected to hold metadata for how
the raid is built, but I may have that wrong.

Greg