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

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Date:	Fri, 12 Apr 2013 16:17:17 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dave Hansen <dave@...1.net>
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

Yes... That is one reason I think it is a real problem.


Dave Hansen <dave@...1.net> 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.

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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