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[79.178.2.214]) by smtp.gmail.com with ESMTPSA id f26sm1053883qtv.77.2020.02.26.05.37.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Feb 2020 05:37:17 -0800 (PST) Date: Wed, 26 Feb 2020 08:37:13 -0500 From: "Michael S. Tsirkin" To: Halil Pasic Subject: Re: [PATCH V2] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM Message-ID: <20200226083654-mutt-send-email-mst@kernel.org> References: <20200226094357.25061-1-jasowang@redhat.com> <20200226142839.4263de9b.pasic@linux.ibm.com> MIME-Version: 1.0 In-Reply-To: <20200226142839.4263de9b.pasic@linux.ibm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jason Wang , qemu-devel@nongnu.org, qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Feb 26, 2020 at 02:28:39PM +0100, Halil Pasic wrote: > On Wed, 26 Feb 2020 17:43:57 +0800 > Jason Wang wrote: >=20 > > We turn on device IOTLB via VIRTIO_F_IOMMU_PLATFORM unconditionally on > > platform without IOMMU support. This can lead unnecessary IOTLB > > transactions which will damage the performance. > >=20 > > Fixing this by check whether the device is backed by IOMMU and disable > > device IOTLB. > >=20 > > Reported-by: Halil Pasic > > Fixes: c471ad0e9bd46 ("vhost_net: device IOTLB support") > > Cc: qemu-stable@nongnu.org > > Signed-off-by: Jason Wang >=20 > Tested-by: Halil Pasic > Reviewed-by: Halil Pasic >=20 > Thank you very much for fixing this! BTW as I mentioned before it > fixes vhost-vsock with iommu_platform=3Don as well. Fixes as in improves performance? > Regards, > Halil >=20 > > --- > > Changes from V1: > > - do not check acked_features > > - reuse vhost_dev_has_iommu() > > --- > > hw/virtio/vhost.c | 12 +++++++++++- > > 1 file changed, 11 insertions(+), 1 deletion(-) > >=20 > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > > index 9edfadc81d..9182a00495 100644 > > --- a/hw/virtio/vhost.c > > +++ b/hw/virtio/vhost.c > > @@ -290,7 +290,14 @@ static int vhost_dev_has_iommu(struct vhost_dev *d= ev) > > { > > VirtIODevice *vdev =3D dev->vdev; > > =20 > > - return virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM); > > + /* > > + * For vhost, VIRTIO_F_IOMMU_PLATFORM means the backend support > > + * incremental memory mapping API via IOTLB API. For platform that > > + * does not have IOMMU, there's no need to enable this feature > > + * which may cause unnecessary IOTLB miss/update trnasactions. > > + */ > > + return vdev->dma_as !=3D &address_space_memory && > > + virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM); > > } > > =20 > > static void *vhost_memory_map(struct vhost_dev *dev, hwaddr addr, > > @@ -765,6 +772,9 @@ static int vhost_dev_set_features(struct vhost_dev = *dev, > > if (enable_log) { > > features |=3D 0x1ULL << VHOST_F_LOG_ALL; > > } > > + if (!vhost_dev_has_iommu(dev)) { > > + features &=3D ~(0x1ULL << VIRTIO_F_IOMMU_PLATFORM); > > + } > > r =3D dev->vhost_ops->vhost_set_features(dev, features); > > if (r < 0) { > > VHOST_OPS_DEBUG("vhost_set_features failed");