Rohit Seth wrote:
On Thu, 2005-11-10 at 00:23 -0800, [email protected] 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 <[email protected]>
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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