[PATCH 5/5] kexec: X86: Pass memory ranges via e820 table instead of memmap= boot parameter
dave at sr71.net
Fri Apr 12 18:17:39 EDT 2013
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.
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