linux-kernel - Re: [Patch] kexec: increase max of kexec segments and use dynamic allocation

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <4C4D5F4F.8080002@redhat.com>
Date:	Mon, 26 Jul 2010 18:11:27 +0800
From:	Cong Wang <amwang@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	huang ying <huang.ying.caritas@...il.com>,
	linux-kernel@...r.kernel.org, nhorman@...hat.com,
	akpm@...ux-foundation.org
Subject: Re: [Patch] kexec: increase max of kexec segments and use dynamic
  allocation

On 07/25/10 10:54, Eric W. Biederman wrote:
> huang ying<huang.ying.caritas@...il.com>  writes:
>
>> On Thu, Jul 22, 2010 at 3:08 PM, Eric W. Biederman
>> <ebiederm@...ssion.com>  wrote:
>>> Cong Wang<amwang@...hat.com>  writes:
>>>
>>>> On 07/22/10 14:28, Eric W. Biederman wrote:
>>>>> Amerigo Wang<amwang@...hat.com>    writes:
>>>>>
>>>>>> Currently KEXEC_SEGMENT_MAX is only 16 which is too small for machine with
>>>>>> many memory ranges. Increase this hard limit to 1024 which is reasonably large,
>>>>>> and change ->segment from a static array to a dynamically allocated memory.
>>>>>
>>>>> ???
>>>>>
>>>>> This should be about segments in the executable being loaded.  What
>>>>> executable has one segment for each range of physical memory?
>>>>>
>>>>> Not that generalizing this is a bad idea but with a comment that
>>>>> seems entirely wrong I am wondering what the problem really is.
>>>>>
>>>>
>>>> Ah, I think Neil should explain this.
>>>>
>>>> He made a patch which includes many memory ranges, caused kexec
>>>> fails to load the kernel. Increasing this limit and the corresponding
>>>> one in kexec-tools fixes the problem. His patch is not in upstream
>>>> kexec-tools, AFAIK.
>>>>
>>>> However, even if we don't consider that patch, isn't 16 too small too?
>>>
>>> Generally you just need one physical hunk for the code, maybe a second
>>> for the initrd.
>>>
>>> It is perfectly fine to raise the number of segments as it doesn't
>>> affect the ABI, but it wants a good explanation of what kind of weird
>>> application wants to write to all over memory when it is loaded.
>>
>> kexec can be used to load not only the kernel images, but also more
>> complex images such as hibernation image. So I think it is good to
>> raise the number of segments.
>
> Totally reasonable.
>
> And in all fairness the patch does a good job of raising the limit.
>
> However if that is the goal 1024 is probably a bit low as I believe
> SGI has built machines with that many nodes.  Still after the patch
> under discussion 1024 was only a limit in a header file so it can
> be trivially changed.

So, what is a better number? 2048? :)

Thanks.

-- 
The opposite of love is not hate, it's indifference.
  - Elie Wiesel
--
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/