[PATCH] ARM: Add SWP/SWPB emulation for ARMv7 processors (v3)

[Russell King - ARM Linux]

On Wed, Jan 06, 2010 at 04:23:47PM +0000, Catalin Marinas wrote:
> On ARMv6 onwards (where this user RO, kernel RO is supported) we cannot
> easily differentiate between the vectors page and a normal kernel page
> unless we use another L_PTE_ bit. We need the vectors page to be
> writable if there is no TLS register in hardware (I guess we could use
> domain switching to override this though). But on ARMv7 we always have a
> TLS register, so no need to write to the vectors page.

That's not the only reason you'd want to write to the vectors page.
You'll want to write to it to install or change FIQ handlers.