x86/mm: Avoid overlap the fixmap area on i386

It is a problem when configuring high memory off where the
vmalloc reserve area could end up overlapping the early_ioremap
fixmap area on i386.

The ordering of the VMALLOC_RESERVE space is:

 FIXADDR_TOP
                       fixed_addresses
 FIXADDR_START
                       early_ioremap fixed addresses
 FIXADDR_BOOT_START
                       Persistent kmap area
 PKMAP_BASE
 VMALLOC_END
                       Vmalloc area
 VMALLOC_START
 high_memory

The available address we can use is lower than
FIXADDR_BOOT_START. So we will set the kmap boundary below the
FIXADDR_BOOT_START, if we configure high memory.

If we configure high memory, the vmalloc reserve area should
end up to PKMAP_BASE, otherwise should end up to
FIXADDR_BOOT_START.

Signed-off-by: Minfei Huang <mnfhuang@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/6B680A9E-6CE9-4C96-934B-CB01DCB58278@gmail.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>