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

[Stefano Garzarella]

On Fri, Oct 30, 2020 at 07:44:43PM +0800, Jason Wang wrote:
> On 2020/10/30 下午6:54, Stefano Garzarella wrote:
> > 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)
>
>
> I guess it's because the batched unmap. Maybe you can try to use 
> "intel_iommu=strict" in guest kernel command line to see if it works.
>
> Btw, make sure the qemu contains the patch [1]. Otherwise ATS won't be 
> enabled for recent Linux Kernel in the guest.

I tried with "intel_iommu=strict" in the guest kernel and QEMU patch 
applied, but I didn't see any invalidation.

Maybe I did something wrong, you know it is friday, KVM Forum is ending, 
etc... ;-)

I'll investigate better next week.

Thanks for the useful info,
Stefano