linux-kernel - Re: [PATCH 5/5] kexec: X86: Pass memory ranges via e820 table instead of memmap= boot parameter

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 12 Apr 2013 15:17:39 -0700
From:	Dave Hansen <dave@...1.net>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Vivek Goyal <vgoyal@...hat.com>, Yinghai Lu <yinghai@...nel.org>,
	Thomas Renninger <trenn@...e.de>,
	Simon Horman <horms@...ge.net.au>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Cliff Wickman <cpw@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] kexec: X86: Pass memory ranges via e820 table instead
 of memmap= boot parameter

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/