From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Mosberger Date: Thu, 03 Feb 2005 03:52:54 +0000 Subject: Re: Abusing region 0 Message-Id: <16897.40982.47145.796311@napali.hpl.hp.com> List-Id: References: <42017845.9080507@free.fr> In-Reply-To: <42017845.9080507@free.fr> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org >>>>> On Thu, 03 Feb 2005 02:03:01 +0100, "Menyhart, Zoltan" said: Zoltan> I am going to do some experiments: I am going to map some of Zoltan> the virtual address ranges of a process into the address Zoltan> space of another one. They are real 64 bit processes, Zoltan> i.e. the region 0 is not used. Can I abuse this region 0 Zoltan> for mapping the addresses of the neighbor process into this Zoltan> region ? E.g. if process A has got an address at Zoltan> 0x6000000000001000, then I am going to map it for B at Zoltan> address 0x0000000000001000 ? Wont anything break ? Zoltan> (I need this trick because the source address can correspond Zoltan> to anything, like initialized data, BSS, anonymous Zoltan> allocation, etc, i.e. some SHM just wont work.) Zoltan> Any advice will be appreciated. Yes, you can do this. There is nothing special about region 0 as far as the kernel is concerned. Well, I'm lying: the one thing that's special is that there is a NaT page mapped at address 0 to catch speculative accesses through a NULL-pointer. Because of that, I'd recommend to use an address greater than 64KB (the largest base page-size supported by Linux). --david