linux-kernel - Re: [PATCH] x86/mm: Limit 2/4M size calculation to x86

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Date:	Fri, 31 Aug 2012 09:56:53 -0700
From:	Stefan Bader <stefan.bader@...onical.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Avi Kivity <avi@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	Konrad Rezeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86/mm: Limit 2/4M size calculation to x86_32

On 08/31/2012 09:41 AM, H. Peter Anvin wrote:
> I'm not saying we shouldn't patch the regression, but this house of cards
> *needs* to be replaced with something robust and correct by construction.

Then I did misunderstand/-interpret you about the former part and we actually 
are agreeing on the whole topic. Sorry about that. So the re-post just should 
serve as a reminder as the last comment here was quite a while ago.

>
> Stefan Bader <stefan.bader@...onical.com> wrote:
>
>> Avi wrote:
>>> The fact that the check is only done on i386 and not on x86_64 may come
>>> from one of
>>>
>>> - an oversight - by the time x86_64 processors came along, the problem
>>> with conflicting sizes was resolved - the whole thing is bogus
>>>
>>> Copying hpa who may be in a position to find out which.
>>
>> Talking to hpa it is more of the last. For more than just this reason.
>> Since the whole area of initial page tables seems to be rather sensitive
>> and easy to break there have been discussions and plans to come up with a
>> rewrite to improve on all those shortcomings.
>>
>> The detail I am not agreeing with hpa is the fixup for the immediate
>> breakage at head. IMO right now the code just has regressed and that should
>> be fixed as soon as possible. Plus doing a specific and small fix allows
>> that to be applicable to stable (which again still depends on things being
>> upstream).
>>
>> Hence the re-send in the hope that on the larger scale the may be agreement
>> on the immediate fix. I am not doubting the usefulness or need of a better
>> solution, but I think that having a remedy of the current situation just
>> until then has enough benefit to be considered.
>>
>> -Stefan

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