From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM Date: Mon, 24 Feb 2020 14:45:03 +0800 Message-ID: References: <20200220160606.53156-1-pasic@linux.ibm.com> <426e6972-0565-c931-e171-da0f58fbf856@redhat.com> <20200221155602.4de41fa7.pasic@linux.ibm.com> <0181712c-e533-fcfd-2638-8a0649d713dd@redhat.com> <20200224010607-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------BCF6A0F752A8D2F33C415C99" Return-path: In-Reply-To: <20200224010607-mutt-send-email-mst@kernel.org> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: "Michael S. Tsirkin" Cc: Halil Pasic , Marek Szyprowski , Robin Murphy , Christoph Hellwig , linux-s390@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Christian Borntraeger , Janosch Frank , Viktor Mihajlovski , Cornelia Huck , Ram Pai , Thiago Jung Bauermann , David Gibson , "Lendacky, Thomas" , Michael Mueller List-Id: virtualization@lists.linuxfoundation.org This is a multi-part message in MIME format. --------------BCF6A0F752A8D2F33C415C99 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2020/2/24 =E4=B8=8B=E5=8D=882:06, Michael S. Tsirkin wrote: > On Mon, Feb 24, 2020 at 12:01:57PM +0800, Jason Wang wrote: >> On 2020/2/21 =E4=B8=8B=E5=8D=8810:56, Halil Pasic wrote: >>> On Fri, 21 Feb 2020 14:22:26 +0800 >>> Jason Wang wrote: >>> >>>> On 2020/2/21 =E4=B8=8A=E5=8D=8812:06, Halil Pasic wrote: >>>>> Currently if one intends to run a memory protection enabled VM with >>>>> virtio devices and linux as the guest OS, one needs to specify the >>>>> VIRTIO_F_IOMMU_PLATFORM flag for each virtio device to make the gue= st >>>>> linux use the DMA API, which in turn handles the memory >>>>> encryption/protection stuff if the guest decides to turn itself int= o >>>>> a protected one. This however makes no sense due to multiple reason= s: >>>>> * The device is not changed by the fact that the guest RAM is >>>>> protected. The so called IOMMU bypass quirk is not affected. >>>>> * This usage is not congruent with standardised semantics of >>>>> VIRTIO_F_IOMMU_PLATFORM. Guest memory protected is an orthogonal re= ason >>>>> for using DMA API in virtio (orthogonal with respect to what is >>>>> expressed by VIRTIO_F_IOMMU_PLATFORM). >>>>> >>>>> This series aims to decouple 'have to use DMA API because my (guest= ) RAM >>>>> is protected' and 'have to use DMA API because the device told me >>>>> VIRTIO_F_IOMMU_PLATFORM'. >>>>> >>>>> Please find more detailed explanations about the conceptual aspects= in >>>>> the individual patches. There is however also a very practical prob= lem >>>>> that is addressed by this series. >>>>> >>>>> For vhost-net the feature VIRTIO_F_IOMMU_PLATFORM has the following= side >>>>> effect The vhost code assumes it the addresses on the virtio descri= ptor >>>>> ring are not guest physical addresses but iova's, and insists on do= ing a >>>>> translation of these regardless of what transport is used (e.g. whe= ther >>>>> we emulate a PCI or a CCW device). (For details see commit 6b1e6cc7= 855b >>>>> "vhost: new device IOTLB API".) On s390 this results in severe >>>>> performance degradation (c.a. factor 10). >>>> Do you see a consistent degradation on the performance, or it only >>>> happen when for during the beginning of the test? >>>> >>> AFAIK the degradation is consistent. >>> >>>>> BTW with ccw I/O there is >>>>> (architecturally) no IOMMU, so the whole address translation makes = no >>>>> sense in the context of virtio-ccw. >>>> I suspect we can do optimization in qemu side. >>>> >>>> E.g send memtable entry via IOTLB API when vIOMMU is not enabled. >>>> >>>> If this makes sense, I can draft patch to see if there's any differe= nce. >>> Frankly I would prefer to avoid IOVAs on the descriptor ring (and the >>> then necessary translation) for virtio-ccw altogether. But Michael >>> voiced his opinion that we should mandate F_IOMMU_PLATFORM for device= s >>> that could be used with guests running in protected mode. I don't sha= re >>> his opinion, but that's an ongoing discussion. >>> >>> Should we end up having to do translation from IOVA in vhost, we are >>> very interested in that translation being fast and efficient. >>> >>> In that sense we would be very happy to test any optimization that ai= m >>> into that direction. >>> >>> Thank you very much for your input! >> >> Using IOTLB API on platform without IOMMU support is not intended. Ple= ase >> try the attached patch to see if it helps. >> >> Thanks >> >> >>> Regards, >>> Halil >>> >>>> Thanks >>>> >>>> >>>>> Halil Pasic (2): >>>>> mm: move force_dma_unencrypted() to mem_encrypt.h >>>>> virtio: let virtio use DMA API when guest RAM is protected >>>>> >>>>> drivers/virtio/virtio_ring.c | 3 +++ >>>>> include/linux/dma-direct.h | 9 --------- >>>>> include/linux/mem_encrypt.h | 10 ++++++++++ >>>>> 3 files changed, 13 insertions(+), 9 deletions(-) >>>>> >>>>> >>>>> base-commit: ca7e1fd1026c5af6a533b4b5447e1d2f153e28f2 >> >From 66fa730460875ac99e81d7db2334cd16bb1d2b27 Mon Sep 17 00:00:00 200= 1 >> From: Jason Wang >> Date: Mon, 24 Feb 2020 12:00:10 +0800 >> Subject: [PATCH] virtio: turn on IOMMU_PLATFORM properly >> >> When transport does not support IOMMU, we should clear IOMMU_PLATFORM >> even if the device and vhost claims to support that. This help to >> avoid the performance overhead caused by unnecessary IOTLB miss/update >> transactions on such platform. >> >> Signed-off-by: Jason Wang >> --- >> hw/virtio/virtio-bus.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c >> index d6332d45c3..2741b9fdd2 100644 >> --- a/hw/virtio/virtio-bus.c >> +++ b/hw/virtio/virtio-bus.c >> @@ -47,7 +47,6 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, E= rror **errp) >> VirtioBusState *bus =3D VIRTIO_BUS(qbus); >> VirtioBusClass *klass =3D VIRTIO_BUS_GET_CLASS(bus); >> VirtioDeviceClass *vdc =3D VIRTIO_DEVICE_GET_CLASS(vdev); >> - bool has_iommu =3D virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_P= LATFORM); >> Error *local_err =3D NULL; >> =20 >> DPRINTF("%s: plug device.\n", qbus->name); >> @@ -77,10 +76,11 @@ void virtio_bus_device_plugged(VirtIODevice *vdev,= Error **errp) >> return; >> } >> =20 >> - if (klass->get_dma_as !=3D NULL && has_iommu) { >> - virtio_add_feature(&vdev->host_features, VIRTIO_F_IOMMU_PLATF= ORM); >> + if (false && klass->get_dma_as !=3D NULL && >> + virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) { >> vdev->dma_as =3D klass->get_dma_as(qbus->parent); >> } else { >> + virtio_clear_feature(&vdev->host_features, VIRTIO_F_IOMMU_PLA= TFORM); >> vdev->dma_as =3D &address_space_memory; >> } >> } > > This seems to clear it unconditionally. I guess it's just a debugging > patch, the real one will come later? My bad, here's the correct one. Thanks > >> --=20 >> 2.19.1 >> --------------BCF6A0F752A8D2F33C415C99 Content-Type: text/x-patch; name="0001-virtio-turn-on-IOMMU_PLATFORM-properly.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="0001-virtio-turn-on-IOMMU_PLATFORM-properly.patch" >From b8a8b582f46bb86c7a745b272db7b744779e5cc7 Mon Sep 17 00:00:00 2001 From: Jason Wang Date: Mon, 24 Feb 2020 12:00:10 +0800 Subject: [PATCH] virtio: turn on IOMMU_PLATFORM properly When transport does not support IOMMU, we should clear IOMMU_PLATFORM even if the device and vhost claims to support that. This help to avoid the performance overhead caused by unnecessary IOTLB miss/update transactions on such platform. Signed-off-by: Jason Wang --- hw/virtio/virtio-bus.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c index d6332d45c3..4be64e193e 100644 --- a/hw/virtio/virtio-bus.c +++ b/hw/virtio/virtio-bus.c @@ -47,7 +47,6 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, Error **errp) VirtioBusState *bus = VIRTIO_BUS(qbus); VirtioBusClass *klass = VIRTIO_BUS_GET_CLASS(bus); VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev); - bool has_iommu = virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM); Error *local_err = NULL; DPRINTF("%s: plug device.\n", qbus->name); @@ -77,10 +76,11 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, Error **errp) return; } - if (klass->get_dma_as != NULL && has_iommu) { - virtio_add_feature(&vdev->host_features, VIRTIO_F_IOMMU_PLATFORM); + if (klass->get_dma_as != NULL && + virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) { vdev->dma_as = klass->get_dma_as(qbus->parent); } else { + virtio_clear_feature(&vdev->host_features, VIRTIO_F_IOMMU_PLATFORM); vdev->dma_as = &address_space_memory; } } -- 2.19.1 --------------BCF6A0F752A8D2F33C415C99--