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X-Comment-To: sridhar vaidyanathan
To: sridhar vaidyanathan <sridharv@ufl.edu>
Cc: linux-kernel@vger.kernel.org
Subject: Re: mmaping /dev/mem
References: <1047515807.3e6fd29f92939@webmail.health.ufl.edu>
From: Alex Tomas <bzzz@tmi.comex.ru>
Organization: HOME
Date: 13 Mar 2003 23:49:59 +0300
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>>>>> sridhar vaidyanathan (sv) writes:

 sv> I have a problem mmaping /dev/mem on some address in RAM. I am
 sv> aware of caveats,but I am trying to mmap a region which I am sure
 sv> is not in use by the kernel(some additional code does this and
 sv> returns a physical address which is what I use for mmap). The
 sv> mmap call itself succeeds and /proc/pid/maps also shows that
 sv> region, but I am unable to see what I write in target memory.I
 sv> also tried with the O_SYNC flag as I was wondering is caching had
 sv> anything to do with the results that I was seeing.No effect.
 sv> This however works with a mem= option and when the mmap region
 sv> falls out of the mem= boundary.  any clues?  Please cc as I am
 sv> not subscribed sridhar

look at mm/memory.c:remap_pte_range():

		if ((!VALID_PAGE(page)) || PageReserved(page))
 			set_pte(pte, mk_pte_phys(phys_addr, prot));

so, your pages aren't mapped at all and pte'es contain zero ...

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