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

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Date:   Fri, 30 Oct 2020 11:54:22 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, netdev@...r.kernel.org,
        Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost/vsock: add IOTLB API support

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