[PATCH 2/2] arm: invalidate TLBs when enabling mmu

[Russell King - ARM Linux]

On Thu, Apr 15, 2010 at 08:24:02PM +0800, Eric Miao wrote:
> Another noticeable difference is the slow decompressing happens so far on
> kexec only, a normal boot without this additional "invalidate" does not
> exhibit such slowness. This leads to me to suspect that the MMU state might
> not be same between a normal bootup and a kexec soft reboot.
> 
> I may overlooked, but it looks to me that after a 1:1 mapping of ther user
> space area (from 0x0000_0000 to TASK_SIZE, which I guess will cause some
> other issue if the kexec kernel start entry starts beyond TASK_SIZE?), the
> MMU is NOT actually turned off through the reset. This might cause weird
> behavior with the original sequence of __armv7_mmu_cache_on ??

For kexec:

        cpu_proc_fin();
        setup_mm_for_reboot(0); /* mode is not used, so just pass 0*/
        cpu_reset(reboot_code_buffer_phys);

cpu_proc_fin() disables interrupts, flushes the cache and then disables
caches.

setup_mm_for_reboot() creates 1:1 mappings for the entire user address
space, which ends up being strongly ordered.

cpu_reset() is supposed to invalidate I/D caches, invalidate TLBs, and
disable the MMU prior to calling the passed address.  However, neither
ARMv6 nor ARMv7 does this - and I'm confused as to why not.