Re: [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM

[Jason Wang]

On 2020/2/24 äå9:40, 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:

ÂÂÂ val &= vdev->host_features;
ÂÂÂ if (k->set_features) {
ÂÂÂÂÂÂÂ k->set_features(vdev, val);
ÂÂÂ }
ÂÂÂ vdev->guest_features = val;

Thanks

>