From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:55545) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SWULl-00046u-AG for qemu-devel@nongnu.org; Mon, 21 May 2012 11:16:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SWULd-0000qi-Pe for qemu-devel@nongnu.org; Mon, 21 May 2012 11:16:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:6771) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SWULd-0000qO-Hi for qemu-devel@nongnu.org; Mon, 21 May 2012 11:16:37 -0400 Message-ID: <4FBA5C38.1020900@redhat.com> Date: Mon, 21 May 2012 17:16:08 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1337565405.2458.12.camel@pasglop> <4FB9F89A.90702@redhat.com> <20120521083132.GI4674@redhat.com> <1337590688.2779.37.camel@pasglop> <1337591230.2779.42.camel@pasglop> <1337591787.2779.48.camel@pasglop> <20120521093440.GK4674@redhat.com> <1337594003.2779.56.camel@pasglop> <20120521103101.GL4674@redhat.com> <1337600758.2779.90.camel@pasglop> <20120521121824.GA8666@redhat.com> In-Reply-To: <20120521121824.GA8666@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] Add a memory barrier to guest memory access functions List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, Anthony Liguori , David Gibson Il 21/05/2012 14:18, Michael S. Tsirkin ha scritto: >> > Almost all our >> > devices were written without any thought given to ordering, so they >> > basically can and should be considered as all broken. > Problem is, a lot of code is likely broken even after you sprinkle > barriers around. For example qemu might write A then B where guest driver > expects to see B written before A. This would be a bug in the guest driver, and usually relatively easy to reproduce. The specs (I know of UHCI) should be very precise on this for obvious reasons. Paolo