linux-kernel - Re: mmap syscall problem

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Date:	Mon, 06 Jul 2009 14:07:06 +0200
From:	Michal Simek <michal.simek@...alogix.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	LTP <ltp-list@...ts.sourceforge.net>,
	John Williams <john.williams@...alogix.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	subrata@...ux.vnet.ibm.com
Subject: Re: mmap syscall problem

Arnd Bergmann wrote:
> On Monday 06 July 2009, Michal Simek wrote:
>   
>>> Does this happen on microblaze-mmu or microblaze-nommu, or both?
>>> The mmap code for the two is very different.
>>>   
>>>       
>> For MMU code.
>>     
>
> Could this be a cache-aliasing problem? If your cache is 'virtually-indexed'
> (most architectures are 'physically-indexed'), the kernel may have written
> into different parts of the D-cache than what the user space is reading
> from. If you have a write-through cache, that can explain why you only
> see the stale data at the beginning of the page -- the cache controller
> is still busy writing back the data when you start reading it from
> DRAM through the cache alias.
>   
I don't think so because we run that test on Microblaze without caches
and test failed too.
I think that this is sufficient test to tell that the problem is not
relate with caches.

Michal

> If this is your problem, then you need to implement flush_dcache_page()
> and other functions that maintain cache consistency. See
> Documentation/cachetlb.txt and http://www.linuxjournal.com/article/7105
>
> 	Arnd <><
>   


-- 
Michal Simek, Ing. (M.Eng)
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663

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