linux-kernel - Re: mmap hw behavior

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Message-Id: <20090708.110624.104984745.davem@davemloft.net>
Date:	Wed, 08 Jul 2009 11:06:24 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	michal.simek@...alogix.com
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	mingo@...e.hu, arnd@...db.de, lethal@...ux-sh.org,
	ltp-list@...ts.sourceforge.net
Subject: Re: mmap hw behavior

From: Michal Simek <michal.simek@...alogix.com>
Date: Wed, 08 Jul 2009 20:03:27 +0200

> David Miller wrote:
>> From: Michal Simek <michal.simek@...alogix.com>
>> Date: Wed, 08 Jul 2009 19:03:11 +0200
>>
>>   
>>> When I call mmap for that open file with pointer to calloc place
>>> (first parameter, + length zero) it should be one tlb invalidation
>>> for calloc and new tlb which connect open file.  We check it and we
>>> don't have any tlb invalidation that's why I think that kernel do
>>> different thigs.  Or is it there any copying? Or anything different?
>>>     
>>
>> There is no need to tlb flush the calloc area unless that memory area
>> is actually touched by the user application and thus the page is
>> faulted in.
>>   
> That calloc area is filled by any value (in that test). Is it mean that
> for this case when calloc area is touched
> there must be tlb invalidation + remapping?

Yes, if the calloc area is written to by the application, there
should be a tlb flush when the mmap() overrides that virtual region
with a different mapping.
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