[Lguest] [PATCH] fix lguest rmmod "bad pgd"

[pageexec at freemail.hu]

(sorry for breaking the thread but i didn't get the original headers)

> After 17d57a9206b4de6ad082ac9f2d2346985abbd2aa
> (x86: fix x86-32 early fixmap initialization.) removing lg.ko caused a
> printk from vunmap:
> 
>  mm/memory.c:115: bad pgd 004b3027.
> 
> On the second use after module load, the kernel crashes.
> 
> This fixes the immediate problem (accessed and dirty bits not set as
> expected in pmd_none_or_clear_bad).  I can't see why this would cause a
> crash, but I haven't been able to reproduce it once this is applied.

it's the 'clear_bad' part that zero's out the pmd and hence destroys
all the fixmap mappings in that 4 MB range leading to page faults at
probably the most unexpected times.