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vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM

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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 <pasic@linux.ibm.com>
Tested-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20200302042454.24814-1-jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Jason Wang 2020-03-02 12:24:54 +08:00 committed by Michael S. Tsirkin
parent 530a096318
commit f7ef7e6e3b
1 changed files with 11 additions and 1 deletions
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12
hw/virtio/vhost.c
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@ -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");