From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34448) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XJ8rg-0006bh-8O for qemu-devel@nongnu.org; Sun, 17 Aug 2014 18:23:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XJ8rX-00072p-82 for qemu-devel@nongnu.org; Sun, 17 Aug 2014 18:23:52 -0400 Received: from mail-la0-f51.google.com ([209.85.215.51]:43685) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XJ8rX-00072H-18 for qemu-devel@nongnu.org; Sun, 17 Aug 2014 18:23:43 -0400 Received: by mail-la0-f51.google.com with SMTP id pn19so3867426lab.38 for ; Sun, 17 Aug 2014 15:23:41 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <5de8cf7083b0e4dabc0692451f2b319badf2b6e0.1408086974.git.peter.crosthwaite@xilinx.com> References: <5de8cf7083b0e4dabc0692451f2b319badf2b6e0.1408086974.git.peter.crosthwaite@xilinx.com> From: Peter Maydell Date: Sun, 17 Aug 2014 23:23:20 +0100 Message-ID: Content-Type: text/plain; charset=UTF-8 Subject: Re: [Qemu-devel] [PATCH memory v1 1/1] memory: remove may_overlap property List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Crosthwaite Cc: Paolo Bonzini , QEMU Developers On 15 August 2014 08:17, Peter Crosthwaite wrote: > In a5e1cbc80e88ed7d73b3fcb46053a3ba167293fc the enforcement of Memory > collisions was disabled. This means that the MemoryRegion map_overlap > state is unused. Remove it completely. > > The commit mentions that it should be fixed, but we have been living > happily-every-after since removal of the check so it's probably > unneeded complication. Um. I think in general colliding memory regions imply a bug in the machine model which is creating them. We have the collisions disabled because nobody's got round to fixing this bug in the PC model yet and it happens to be harmless there. I'm not really convinced that yanking out the check code is better than fixing the PC model... > If we were to repair this, a simpler and more effective check would be > to only assert collisions between same-priority regions. The fact that > colliding memory regions may-overlap is then left as implicit by the > fact that they have different priorities. I'm not sure your suggestion here would work, because priorities are only significant relative to other regions within the same container, whereas collisions can occur between two regions which don't have the same parent container and whose priorities are therefore not comparable. (For instance, consider [ A [ B C ] ] where A and B end up overlapping.) thanks -- PMM