From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 21 Feb 2008 05:42:56 +0100 From: Nick Piggin Subject: Re: [patch] my mmu notifiers Message-ID: <20080221044256.GA15215@wotan.suse.de> References: <20080219084357.GA22249@wotan.suse.de> <20080219135851.GI7128@v2.random> <20080219231157.GC18912@wotan.suse.de> <20080219234049.GA27856@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080219234049.GA27856@sgi.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Jack Steiner Cc: Andrea Arcangeli , akpm@linux-foundation.org, Robin Holt , Avi Kivity , Izik Eidus , kvm-devel@lists.sourceforge.net, Peter Zijlstra , general@lists.openfabrics.org, Steve Wise , Roland Dreier , Kanoj Sarcar , linux-kernel@vger.kernel.org, linux-mm@kvack.org, daniel.blueman@quadrics.com, Christoph Lameter List-ID: On Tue, Feb 19, 2008 at 05:40:50PM -0600, Jack Steiner wrote: > On Wed, Feb 20, 2008 at 12:11:57AM +0100, Nick Piggin wrote: > > On Tue, Feb 19, 2008 at 02:58:51PM +0100, Andrea Arcangeli wrote: > > > On Tue, Feb 19, 2008 at 09:43:57AM +0100, Nick Piggin wrote: > > > > anything when changing the pte to be _more_ permissive, and I don't > > > > > > Note that in my patch the invalidate_pages in mprotect can be > > > trivially switched to a mprotect_pages with proper params. This will > > > prevent page faults completely in the secondary MMU (there will only > > > be tlb misses after the tlb flush just like for the core linux pte), > > > and it'll allow all the secondary MMU pte blocks (512/1024 at time > > > with my PT lock design) to be updated to have proper permissions > > > matching the core linux pte. > > > > Sorry, I realise I still didn't get this through my head yet (and also > > have not seen your patch recently). So I don't know exactly what you > > are doing... > > > > But why does _anybody_ (why does Christoph's patches) need to invalidate > > when they are going to be more permissive? This should be done lazily by > > the driver, I would have thought. > > > Agree. Although for most real applications, the performance difference > is probably negligible. But importantly, doing it that way means you share test coverage with the CPU TLB flushing code, and you don't introduce a new concept to the VM. So, it _has_ to be lazy flushing, IMO (as there doesn't seem to be a good reason otherwise). mprotect shouldn't really be a special case, because it still has to flush the CPU tlbs as well when restricting access. -- 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: email@kvack.org