[PATCH][AArch64] [AArch64][libgloss] Clear WXN bit from SCTLR_EL3 when initialising page tables

[Kyrill Tkachov]

Hi all,

In ARMv8 cores on reset the WXN bit from SCTLR_EL3 can be set by the core (the 
architecture says that on reset it's UNKNOWN, so the core can do whatever it 
wants). If we don't clear it all memory regions with write permissions will be 
marked as non-executable, potentially causing a permission fault in the startup 
code.

This patch clears that bit and adds a dsb to ensure that everything is committed 
properly.

Tested aarch64-none-elf on a model with no problems.

Ok to go in?

Thanks,
Kyrill

P.S. If this is approved can somebody please commit it for me?

[libgloss/]
2014-01-24  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     * aarch64/cpu-init/rdimon-aem-el3.S (flat_map): Clear WXN bit
     in SCTLR_EL3. Add dsb.
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