linux-kernel - Re: Have any influence on set_memory

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Date:	Thu, 14 Jan 2016 20:35:45 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Mark Rutland <mark.rutland@....com>
CC:	zhong jiang <zhongjiang@...wei.com>,
	Laura Abbott <labbott@...oraproject.org>,
	Hanjun Guo <guohanjun@...wei.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Have any influence on set_memory_** about below patch ??

On 2016/1/13 19:18, Mark Rutland wrote:

> On Wed, Jan 13, 2016 at 06:30:06PM +0800, Xishi Qiu wrote:
>> Hi Mark,
>>
>> If I create swapper page tables by 4kb, not large page, then I use
>> set_memory_ro() to change the pate table flag, does it have the problem
>> too?
> 
> The splitting/merging problem would not apply.
> 
> However, you're going to waste a reasonable amount of memory by not
> using section mappings in the swapper, and we gain additional complexity
> in the page table setup code (which is shared with others things that
> want section mappings).
> 
> What are you exactly actually trying to achieve?
> 

If module allocates some pages and save data on them, and the data will
not be changed during the module running. So we want to use set_memory_ro()
to increase the security. If the data is changed, we can catch someone.

> What memory do you want to mark RO, and why?
> 

The key data, and it will not be changed during the running time.

>>>From a previous discussion [1], we figured out alternative approaches
> for common cases. Do none of those work for your case?
> 

I have not read the patchset carefully, could you tell me the general meaning
of the approaches?

Thanks,
Xishi Qiu

> Thanks,
> Mark.
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-January/397320.html
> 
> .
>