From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH] prevent NULL mmap in topdown model From: Arjan van de Ven In-Reply-To: <20050519064657.GH23013@shell0.pdx.osdl.net> References: <20050519064657.GH23013@shell0.pdx.osdl.net> Content-Type: text/plain Date: Thu, 19 May 2005 10:15:10 +0200 Message-Id: <1116490511.6027.25.camel@laptopd505.fenrus.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Chris Wright Cc: Linus Torvalds , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Wed, 2005-05-18 at 23:46 -0700, Chris Wright wrote: > * Linus Torvalds (torvalds@osdl.org) wrote: > > However, it would be good to have even the trivial patch tested. > > Especially since what it tries to fix is a total corner-case in the first > > place.. > > I gave it a quick and simple test. Worked as expected. Last page got > mapped at 0x1000, leaving first page unmapped. Of course, either with > MAP_FIXED or w/out MAP_FIXED but proper hint (like -1) you can still > map first page. This isn't to say I was extra creative in testing. sure. Making it *impossible* to mmap that page is bad. People should be able to do that if they really want to, just doing it if they don't ask for it is bad. There are plenty of reasons people may want that page mmaped, one of them being that the compiler can then do more speculative loads around null pointer checks. Not saying it's a brilliant idea always, but making such things impossible makes no sense. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org