Cross-CPU TLB flush problem with Fiasco.OC (r56, r58; exynos5)

Hello,

I had a situation where CPU 1 accessed the wrong (same as before)
physical memory location after it was idle while CPU 0 unmapped the
memory page and mapped a different page at the same virtual address
afterwards.

When a CPU is idle, its TLB gets marked as 'inactive' in the kernel and
the CPU doesn't receive cross-CPU TLB flush requests during this time.
It seems there is a TLB flush missing somewhere after CPU 1 leaves the
idle thread, to compensate for any missed flush requests during the idle
time.

When I added a 'Mem_unit::tlb_flush()' call after 'enable_tlb(cpu)' in
'Kernel_thread::idle_op()' as a test, this problem did not occur anymore.

Christian