On 2020/2/24 下午9:40, Michael S. Tsirkin wrote:
Subject: [PATCH] vhost: do not set VIRTIO_F_IOMMU_PLATFORM when IOMMU is not
used
We enable device IOTLB unconditionally when VIRTIO_F_IOMMU_PLATFORM is
negotiated. This lead unnecessary IOTLB miss/update transactions when
IOMMU is used. This patch fixes this.
Signed-off-by: Jason Wang<jasowang@xxxxxxxxxx>
---
hw/net/virtio-net.c | 3 +++
hw/virtio/vhost.c | 4 +---
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 3627bb1717..0d50e8bd34 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -879,6 +879,9 @@ static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features)
virtio_net_apply_guest_offloads(n);
}
+ if (vdev->dma_as == &address_space_memory)
+ features &= ~(1ULL << VIRTIO_F_IOMMU_PLATFORM);
+
for (i = 0; i < n->max_queues; i++) {
NetClientState *nc = qemu_get_subqueue(n->nic, i);
This pokes at acked features. I think they are also
guest visible ...
It's the acked features of vhost device, so I guess not?
E.g virtio_set_features_nocheck() did:
val &= vdev->host_features;
if (k->set_features) {
k->set_features(vdev, val);
}
vdev->guest_features = val;
Thanks
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