On Fri, Jan 28, 2011 at 09:46:06AM +0000, Catalin Marinas wrote:

Does this mean that we could still configure a kernel to run on CPU_V6
with domains disabled? The vectors page becomes read-only and setting
the TLS would fail.

Yes it will, so that's not acceptable either.

My point is that we may want SWP_EMULATE disabled (or depending on !
CPU_USE_DOMAINS). With domains enabled every read-only user page is
writeable by the kernel. This has the side-effect that SWP emulation
using LDREX/STREX breaks COW.

Yes, and maybe we should instead just enable the SWP instruction by default
on ARMv7, and if SWP emulation is built, disable it at that point.

We could change early_trap_init() to always use the vectors_page rather
than the high mapping and determine at run-time (patch the code) whether
set_pte_ext sets R/W kernel permissions for RO user pages.

With aliasing caches that becomes much more difficult.