> Subject: Re: [EXTERNAL] Re: [PATCH] virtio: vdpa: vDPA driver for Marvell
> OCTEON DPU devices
>
> On Wed, Apr 10, 2024 at 10:15:37AM +0000, Srujana Challa wrote:
> > > > > > +
> > > > > > + domain = iommu_get_domain_for_dev(dev);
> > > > > > + if (!domain || domain->type == IOMMU_DOMAIN_IDENTITY) {
> > > > > > + dev_info(dev, "NO-IOMMU\n");
> > > > > > + octep_vdpa_ops.set_map = octep_vdpa_set_map;
> > > > >
> > > > > Is this a shortcut to have get better performance? DMA API
> > > > > should have those greacefully I think.
> > > > When IOMMU is disabled on host and set_map/dma_map is not set,
> > > > vhost-vdpa is reporting an error "Failed to allocate domain,
> > > > device is not
> > > IOMMU cache coherent capable\n".
> > > > Hence we are doing this way to get better performance.
> > >
> > > The problem is, assuming the device does not have any internal IOMMU.
> > >
> > > 1) If we allow it running without IOMMU, it opens a window for guest
> > > to attack the host.
> > > 2) If you see perforamnce issue with IOMMU_DOMAIN_IDENTITY, let's
> > > report it to DMA/IOMMU maintiner to fix that
> > It will be helpful for host networking case when iommu is disabled.
> > Can we take the vfio pci driver approach as a reference where user
> > explicitly set "enable_unsafe_noiommu_mode" using module param?
>
> vfio is a userspace driver so it's userspace's responsibility.
> what exactly ensures correctness here? does the device have an on-chip
> iommu?
>
Our device features an on-chip IOMMU, although it is not utilized for host-side
targeted DMA operations. We included no-iommu mode in our driver to ensure
that host applications, such as DPDK Virtio user PMD, continue to function even
when operating in a no-IOMMU mode. We observed performance impacts on
certain low-end x86 machines when IOMMU mode was enabled.
I think, correctness is Host userspace application's responsibility, in this case
when vhost-vdpa is used with Host application such as DPDK Virtio user PMD.
> > >
> > > Thanks
> >
> > Thanks.
> >
