(2013/04/13 7:17), Dave Hansen wrote: > 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. This sounds like there's no such issue on x86 cache mechanism. Is it correct? If so, what is the difference between ia64 and x86 cache mechanisms? -- Thanks. HATAYAMA, Daisuke
