From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33142) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cLLIh-0002RZ-Sj for qemu-devel@nongnu.org; Sun, 25 Dec 2016 21:46:12 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cLLId-0005yZ-0G for qemu-devel@nongnu.org; Sun, 25 Dec 2016 21:46:11 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54078) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cLLIc-0005y1-O7 for qemu-devel@nongnu.org; Sun, 25 Dec 2016 21:46:06 -0500 References: <1482400096-23078-1-git-send-email-peterx@redhat.com> <20161222110412.GB26435@pxdev.xzpeter.org> <6798718b-3949-032f-0e5f-fa6b2e2d83fb@redhat.com> <20161223032601.GC26435@pxdev.xzpeter.org> From: Jason Wang Message-ID: Date: Mon, 26 Dec 2016 10:45:55 +0800 MIME-Version: 1.0 In-Reply-To: <20161223032601.GC26435@pxdev.xzpeter.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v3] intel_iommu: allow dynamic switch of IOMMU region List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Xu Cc: tianyu.lan@intel.com, kevin.tian@intel.com, mst@redhat.com, jan.kiszka@siemens.com, bd.aviv@gmail.com, qemu-devel@nongnu.org, alex.williamson@redhat.com, david@gibson.dropbear.id.au On 2016=E5=B9=B412=E6=9C=8823=E6=97=A5 11:26, Peter Xu wrote: > On Thu, Dec 22, 2016 at 07:34:10PM +0800, Jason Wang wrote: >> >> On 2016=E5=B9=B412=E6=9C=8822=E6=97=A5 19:04, Peter Xu wrote: >>> On Thu, Dec 22, 2016 at 05:52:58PM +0800, Jason Wang wrote: >>>> On 2016=E5=B9=B412=E6=9C=8822=E6=97=A5 17:48, Peter Xu wrote: >>>>> /* Handle Translation Enable/Disable */ >>>>> static void vtd_handle_gcmd_te(IntelIOMMUState *s, bool en) >>>>> { >>>>> + if (s->dmar_enabled =3D=3D en) { >>>>> + return; >>>>> + } >>>>> + >>>>> VTD_DPRINTF(CSR, "Translation Enable %s", (en ? "on" : "off")= ); >>>>> if (en) { >>>>> @@ -1196,6 +1237,8 @@ static void vtd_handle_gcmd_te(IntelIOMMUStat= e *s, bool en) >>>>> /* Ok - report back to driver */ >>>>> vtd_set_clear_mask_long(s, DMAR_GSTS_REG, VTD_GSTS_TES, 0= ); >>>>> } >>>>> + >>>>> + vtd_switch_address_space_all(s, en); >>>>> } >>>> We may need something like notifier here to tell e.g vhost to stop d= evice >>>> IOTLB. (Since it's likely this series were applied after device IOTL= B >>>> patches) >>> Yes, I missed vhost case. >>> >>> To notify vhost, IMO we should be able to use memory listeners just >>> like how vfio devices do (please refer to vfio_memory_listener). >> Just for switching? This seems an overkill since we don't depends on i= t for >> all other things. Guest should setup correct mappings by explicitly no= tify >> device IOTLB. A quick glance at ATS spec, for enabling and disabling, = looks >> like it was done through enable bit of ASTctl instead of here. >> >> So we are probably ok here :) > So we need a more general way to notify ATS about this, right? (e.g., > for future devices that support ATS as well, not only vhost) Yes, if we want to make ATS visible to guest. But looks like it needs=20 more e.g VFIO support for device IOTLB invalidation. > >>> However, I think the bigger issue is we still don't have a dynamic wa= y >>> to turn vhost DMAR on/off, right? >> The API was ready for this, just issue another set_feature ioctl witho= ut >> IOMMU_PLATFORM. (But unfortunately, vhost need a small patch to make t= his >> work). > That'll be nice. :) > >>> If so, we may need to re-touch all the parts to enable the dynamic >>> switching of DMA remapping - QEMU vhost, kernel vhost, and virtio on >>> the guest side... I start to doubt whether that effort will worth it >>> due to this single change, especially if this feature (dynamic on/off >>> DMA remapping) won't be used by most VMs (i.e., Linux should only tur= n >>> VT-d on when kernel detects it, and should never turn it off in >>> anyway). >> For vhost part, the changes should be very minor, probably just: >> >> - a patch to make sure vhost can disable device IOTLB during feature s= et >> - properly handling enabling bit of ATSctl in qemu (probably through a= n >> notifier) > Do you think I should provide another patch for the domain switch > notification (along with this one)? Or I can just postpone this patch > until DMAR series merged (after all this patch is not an urgent one). My understanding is, at least device IOTLB does not care about this. So=20 we can leave it as is. Thanks