dd if=/dev/mem can hang a machine?

[Andriy Gapon]

I have a new machine with DG33TL mainboard (ICH9/G33).
In a course of some hacking I ran dd if=/dev/mem ... to scan all memory,
this caused the machine to hang.
I tried to reproduce and this is 100% reproducible.

I am not used to such behavior. In older days I could scan all the
memory without any issues.

Could this be related to some modern form of memory-mapped IO? Or to
Intel Management Engine (that seems t bite into DRAM)?
Or something else?

Just wondering.

-- 
Andriy Gapon