Re: [PATCH] vhost/vsock: add IOTLB API support

[Stefano Garzarella]

On Fri, Oct 30, 2020 at 06:02:18PM +0800, Jason Wang wrote:
> On 2020/10/30 上午1:43, Stefano Garzarella wrote:
> > This patch enables the IOTLB API support for vhost-vsock devices,
> > allowing the userspace to emulate an IOMMU for the guest.
> >
> > These changes were made following vhost-net, in details this patch:
> > - exposes VIRTIO_F_ACCESS_PLATFORM feature and inits the iotlb
> >   device if the feature is acked
> > - implements VHOST_GET_BACKEND_FEATURES and
> >   VHOST_SET_BACKEND_FEATURES ioctls
> > - calls vq_meta_prefetch() before vq processing to prefetch vq
> >   metadata address in IOTLB
> > - provides .read_iter, .write_iter, and .poll callbacks for the
> >   chardev; they are used by the userspace to exchange IOTLB messages
> >
> > This patch was tested with QEMU and a patch applied [1] to fix a
> > simple issue:
> >     $ qemu -M q35,accel=kvm,kernel-irqchip=split \
> >            -drive file=fedora.qcow2,format=qcow2,if=virtio \
> >            -device intel-iommu,intremap=on \
> >            -device vhost-vsock-pci,guest-cid=3,iommu_platform=on
>
>
> Patch looks good, but a question:
>
> It looks to me you don't enable ATS which means vhost won't get any 
> invalidation request or did I miss anything?

You're right, I didn't see invalidation requests, only miss and updates.
Now I have tried to enable 'ats' and 'device-iotlb' but I still don't 
see any invalidation.

How can I test it? (Sorry but I don't have much experience yet with 
vIOMMU)

Thanks,
Stefano