the attached pae-2.4.3-C3 patch fixes the PAE code to work with SLAB
FORCED_DEBUG (which enables redzoning) too.

the problem is that redzoning is enabled unconditionally, and SLAB has no
information about how crutial alignment is in the case of any particular
SLAB cache. The CPU generates a general protection fault if in PAE mode a
non-16-byte aligned pgd is loaded into %cr3.

Redzoning is very useful and most caches use HWCACHE_ALIGN, so i didnt
want to disable redzoning if SLAB_HWCACHE_ALIGN is set. The patch adds
SLAB_MUST_HWCACHE_ALIGN, which makes the distinction.

the patch is against 2.4.3-pre8 (applies cleanly to ac26 as well), and
compiles & boot cleanly in PAE mode, with or without CONFIG_DEBUG_SLAB.
The kernel also compiles cleanly in non-PAE mode.

(the patch also introduces the pae_pgd SLAB cache, which is a tiny
speedup.)

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