From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33232) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cVZ5H-0003L3-2v for qemu-devel@nongnu.org; Mon, 23 Jan 2017 02:30:35 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cVZ5C-0005qn-1Z for qemu-devel@nongnu.org; Mon, 23 Jan 2017 02:30:35 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44260) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cVZ5B-0005qW-SH for qemu-devel@nongnu.org; Mon, 23 Jan 2017 02:30:29 -0500 Date: Mon, 23 Jan 2017 15:30:20 +0800 From: Peter Xu Message-ID: <20170123073020.GI26526@pxdev.xzpeter.org> References: <1484917736-32056-1-git-send-email-peterx@redhat.com> <1484917736-32056-20-git-send-email-peterx@redhat.com> <20170122090958.GC26526@pxdev.xzpeter.org> <33026fc1-3649-0d33-2bf1-6260daedfe03@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <33026fc1-3649-0d33-2bf1-6260daedfe03@redhat.com> 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: Jason Wang 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 Mon, Jan 23, 2017 at 09:57:23AM +0800, Jason Wang wrote: >=20 >=20 > 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 = does > >>>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 clear= ed > >>>before replaying the new one. > >>I'm not quite sure this is needed. I thought the only thing we need t= o do is > >>stop DMA of device during the moving? Or is there an example that wil= l 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), >=20 > I thought driver should do this work instead of device, because only dr= iver > knows whether or not iova is still needed? Do you mean "device driver" above? I don't know whether I understood the question above, but the problem should be there no matter which one is managing iova? Thanks, -- peterx