From e06655cfe0fa9473b1e8b311571f36d787472834 Mon Sep 17 00:00:00 2001 From: Thomas Huth Date: Fri, 29 May 2020 05:54:02 -0400 Subject: [PATCH 20/42] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM RH-Author: Thomas Huth Message-id: <20200529055420.16855-21-thuth@redhat.com> Patchwork-id: 97041 O-Subject: [RHEL-8.3.0 qemu-kvm PATCH v2 20/38] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM Bugzilla: 1828317 RH-Acked-by: Claudio Imbrenda RH-Acked-by: Cornelia Huck RH-Acked-by: David Hildenbrand From: Jason Wang 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 Tested-by: Halil Pasic Reviewed-by: Halil Pasic Signed-off-by: Jason Wang Message-Id: <20200302042454.24814-1-jasowang@redhat.com> Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin (cherry picked from commit f7ef7e6e3ba6e994e070cc609eb154339d1c4a11) Signed-off-by: Danilo C. L. de Paula --- 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"); -- 2.27.0