From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43683) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cVTt1-0003rz-LO for qemu-devel@nongnu.org; Sun, 22 Jan 2017 20:57:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cVTsw-0000fH-Py for qemu-devel@nongnu.org; Sun, 22 Jan 2017 20:57:35 -0500 Received: from mx1.redhat.com ([209.132.183.28]:42498) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cVTsw-0000fD-Ju for qemu-devel@nongnu.org; Sun, 22 Jan 2017 20:57:30 -0500 References: <1484917736-32056-1-git-send-email-peterx@redhat.com> <1484917736-32056-20-git-send-email-peterx@redhat.com> <20170122090958.GC26526@pxdev.xzpeter.org> From: Jason Wang Message-ID: <33026fc1-3649-0d33-2bf1-6260daedfe03@redhat.com> Date: Mon, 23 Jan 2017 09:57:23 +0800 MIME-Version: 1.0 In-Reply-To: <20170122090958.GC26526@pxdev.xzpeter.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH RFC v4 19/20] intel_iommu: unmap existing pages before replay List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Xu Cc: qemu-devel@nongnu.org, tianyu.lan@intel.com, kevin.tian@intel.com, mst@redhat.com, jan.kiszka@siemens.com, alex.williamson@redhat.com, bd.aviv@gmail.com On 2017=E5=B9=B401=E6=9C=8822=E6=97=A5 17:09, Peter Xu wrote: > On Sun, Jan 22, 2017 at 04:13:32PM +0800, Jason Wang wrote: >> >> On 2017=E5=B9=B401=E6=9C=8820=E6=97=A5 21:08, Peter Xu wrote: >>> Previous replay works for domain switch only if the original domain d= oes >>> not have mapped pages. For example, if we switch domain from A to B, = it >>> will only work if A has no existing mapping. If there is, then there'= s >>> problem - current replay didn't make sure the old mappings are cleare= d >>> before replaying the new one. >> I'm not quite sure this is needed. I thought the only thing we need to= do is >> stop DMA of device during the moving? Or is there an example that will= cause >> trouble? > I think this patch is essential. > > Example: > > - device D1 moved to domain A, domain A has no mapping > - map page P1 in domain A, so D1 will have a mapping of page P1 > - create domain B with mapping P2 > - move D1 from domain A to domain B > > Here if we don't unmap existing pages in domain A (P1), I thought driver should do this work instead of device, because only=20 driver knows whether or not iova is still needed? Thanks > after the > switch, we'll have D1 with both P1/P2 mapped, while domain B actually > only has P2. That's unaligned mapping, and it should be wrong. > > If you (or anyone) think this is a bug as well for patch 18, I can > just squash both 19/20 into patch 18. > > Thanks, > > -- peterx