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

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Message-ID: <516B87A6.9080708@jp.fujitsu.com>
Date:	Mon, 15 Apr 2013 13:52:54 +0900
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	Dave Hansen <dave@...1.net>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Cliff Wickman <cpw@....com>, Simon Horman <horms@...ge.net.au>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Thomas Renninger <trenn@...e.de>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 5/5] kexec: X86: Pass memory ranges via e820 table instead
 of memmap= boot parameter

(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

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