* Does anyone undefine APM_RELAX_SEGMENTS?
[not found] ` <1132024003.6760.16.camel@akash.sc.intel.com>
@ 2005-11-15 4:04 ` Zachary Amsden
0 siblings, 0 replies; only message in thread
From: Zachary Amsden @ 2005-11-15 4:04 UTC (permalink / raw)
To: Rohit Seth
Cc: akpm, sfr, mm-commits, Linux Kernel Mailing List,
Stephen Rothwell, sfr, david, kontakt
Rohit Seth wrote:
>On Thu, 2005-11-10 at 00:23 -0800, akpm@osdl.org wrote:
>
>
>>The patch titled
>>
>> x86: Always relax segments
>>
>>has been added to the -mm tree. Its filename is
>>
>> x86-always-relax-segments.patch
>>
>>
>>From: Zachary Amsden <zach@vmware.com>
>>
>>APM BIOSes have many bugs regarding proper representation of the appropriate
>>segment limits for calling the BIOS. By default, APM_RELAX_SEGMENTS is always
>>turned on to support running the APM BIOS on these buggy machines. Keeping
>>64k limits poses very little danger to the kernel, because the pages where the
>>APM BIOS is located will always be in low physical memory BIOS areas, which
>>should already be marked reserved, and only buggy BIOSes would possibly
>>overstep the segment bounds with writes to data anyway.
>>
>>Since forcing stricter limits breaks many machines and is not default
>>behavior, it seems reasonable to deprecate the older code which may cause APM
>>BIOS to fault.
>>
>>
>>
>
>But I presume it make some other machines to work?
>
>
It would make the APM thread panic on machines with broken APM BIOS -
which is not very useful except for proving a BIOS bug. But APM is
inherently safer than PnP, since there is no transfer segment which can
corrupt arbitrary kernel memory.
In the history of its introduction, I can not find a single distribution
or use which undefines this macro. If anyone knows otherwise, please
advise.
Zach
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