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From e06655cfe0fa9473b1e8b311571f36d787472834 Mon Sep 17 00:00:00 2001
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From: Thomas Huth <thuth@redhat.com>
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Date: Fri, 29 May 2020 05:54:02 -0400
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Subject: [PATCH 20/42] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM
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RH-Author: Thomas Huth <thuth@redhat.com>
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Message-id: <20200529055420.16855-21-thuth@redhat.com>
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Patchwork-id: 97041
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O-Subject: [RHEL-8.3.0 qemu-kvm PATCH v2 20/38] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM
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Bugzilla: 1828317
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RH-Acked-by: Claudio Imbrenda <cimbrend@redhat.com>
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RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
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RH-Acked-by: David Hildenbrand <david@redhat.com>
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From: Jason Wang <jasowang@redhat.com>
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We turn on device IOTLB via VIRTIO_F_IOMMU_PLATFORM unconditionally on
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platform without IOMMU support. This can lead unnecessary IOTLB
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transactions which will damage the performance.
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Fixing this by check whether the device is backed by IOMMU and disable
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device IOTLB.
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Reported-by: Halil Pasic <pasic@linux.ibm.com>
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Tested-by: Halil Pasic <pasic@linux.ibm.com>
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Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
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Signed-off-by: Jason Wang <jasowang@redhat.com>
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Message-Id: <20200302042454.24814-1-jasowang@redhat.com>
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Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
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Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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(cherry picked from commit f7ef7e6e3ba6e994e070cc609eb154339d1c4a11)
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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hw/virtio/vhost.c | 12 +++++++++++-
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1 file changed, 11 insertions(+), 1 deletion(-)
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diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
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index 9edfadc81d..9182a00495 100644
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--- a/hw/virtio/vhost.c
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+++ b/hw/virtio/vhost.c
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@@ -290,7 +290,14 @@ static int vhost_dev_has_iommu(struct vhost_dev *dev)
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{
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VirtIODevice *vdev = dev->vdev;
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- return virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
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+ /*
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+ * For vhost, VIRTIO_F_IOMMU_PLATFORM means the backend support
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+ * incremental memory mapping API via IOTLB API. For platform that
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+ * does not have IOMMU, there's no need to enable this feature
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+ * which may cause unnecessary IOTLB miss/update trnasactions.
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+ */
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+ return vdev->dma_as != &address_space_memory &&
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+ virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
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}
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static void *vhost_memory_map(struct vhost_dev *dev, hwaddr addr,
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@@ -765,6 +772,9 @@ static int vhost_dev_set_features(struct vhost_dev *dev,
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if (enable_log) {
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features |= 0x1ULL << VHOST_F_LOG_ALL;
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}
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+ if (!vhost_dev_has_iommu(dev)) {
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+ features &= ~(0x1ULL << VIRTIO_F_IOMMU_PLATFORM);
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+ }
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r = dev->vhost_ops->vhost_set_features(dev, features);
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if (r < 0) {
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VHOST_OPS_DEBUG("vhost_set_features failed");
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--
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2.27.0
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