Mapping of ZONE_HIGHMEM in kernel address space in 32bit x86

[Valdis.Kletnieks at vt.edu]

On Tue, 14 May 2013 11:15:35 +0530, Paul Davies C said:

> It is an arbitrary question that popped in my mind. However, I came to know
> that the constraints I stated in the previous mail is only restricted to
> x86 only.Now besides my first questions , I have one more question, Why x86
> only?

It's architecture dependent.  X86 has a lot of legacy crap that most other
archs never had to deal with (for instance, I/O controllers that could only do
DMA under the 16M line because they only supported 24 address lines). Most
other archs have either been design stable (for example alpha), or they did it
mostly right the first time.  X86 is the only major arch that's really grown
from 16 bit to 32 to 64, accumulating cruft all the way.

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