On 04/12/2013 07:56 AM, H. Peter Anvin wrote: > On 04/12/2013 07:31 AM, Vivek Goyal wrote: >>> I also have to admit that I don't see the difference between /dev/mem >>> and /dev/oldmem, as the former allows access to memory ranges outside >>> the ones used by the current kernel, which is what the oldmem device >>> seems to be intended to od. It varies from arch to arch of course. But, /dev/mem has restrictions on it, like CONFIG_STRICT_DEVMEM or the ARCH_HAS_VALID_PHYS_ADDR_RANGE. There's a lot of stuff that depends on it, *and* folks have tried to fix it up so that it's not _as_ blatant of a way to completely screw your system. /dev/mem also tries to be nice to arches that have restrictions like: > /* > * On ia64 if a page has been mapped somewhere as > * uncached, then it must also be accessed uncached > * by the kernel or data corruption may occur > */ I think /dev/oldmem isn't so nice and could actually cause some real problems if used on ia64 where the cached/uncached accesses are mixed.
