On Wed, 26 Feb 2020 17:43:57 +0800 Jason Wang <jasow...@redhat.com> wrote:
> 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. > > Fixing this by check whether the device is backed by IOMMU and disable > device IOTLB. > > Reported-by: Halil Pasic <pa...@linux.ibm.com> > Fixes: c471ad0e9bd46 ("vhost_net: device IOTLB support") > Cc: qemu-sta...@nongnu.org > Signed-off-by: Jason Wang <jasow...@redhat.com> Tested-by: Halil Pasic <pa...@linux.ibm.com> Reviewed-by: Halil Pasic <pa...@linux.ibm.com> Thank you very much for fixing this! BTW as I mentioned before it fixes vhost-vsock with iommu_platform=on as well. Regards, Halil > --- > 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(-) > > 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 *dev) > { > VirtIODevice *vdev = dev->vdev; > > - 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 != &address_space_memory && > + virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM); > } > > 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 |= 0x1ULL << VHOST_F_LOG_ALL; > } > + if (!vhost_dev_has_iommu(dev)) { > + features &= ~(0x1ULL << VIRTIO_F_IOMMU_PLATFORM); > + } > r = dev->vhost_ops->vhost_set_features(dev, features); > if (r < 0) { > VHOST_OPS_DEBUG("vhost_set_features failed");