On Fri, Apr 12, 2024 at 1:13 PM Srujana Challa <schalla@xxxxxxxxxxx> wrote:
>
>
>
> > -----Original Message-----
> > From: Jason Wang <jasowang@xxxxxxxxxx>
> > Sent: Thursday, April 11, 2024 11:32 AM
> > To: Srujana Challa <schalla@xxxxxxxxxxx>
> > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>; virtualization@xxxxxxxxxxxxxxx;
> > xuanzhuo@xxxxxxxxxxxxxxxxx; Vamsi Krishna Attunuru
> > <vattunuru@xxxxxxxxxxx>; Shijith Thotton <sthotton@xxxxxxxxxxx>; Nithin
> > Kumar Dabilpuram <ndabilpuram@xxxxxxxxxxx>; Jerin Jacob
> > <jerinj@xxxxxxxxxxx>; eperezma <eperezma@xxxxxxxxxx>
> > Subject: Re: [EXTERNAL] Re: [PATCH] virtio: vdpa: vDPA driver for Marvell
> > OCTEON DPU devices
> >
> > On Wed, Apr 10, 2024 at 8:35 PM Srujana Challa <schalla@xxxxxxxxxxx>
> > wrote:
> > >
> > > > 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.
> >
> > I may miss something but set_map() is empty in this driver. How could such
> > isolation be done?
>
> In no-iommu case, there would be no domain right, and the user of vhost-vdpa(DPDK virtio user pmd),
> would create the mapping and pass the PA (= IOVA) to the device directly. So that, device can directly
> DMA to the PA.
Yes, but this doesn't differ too much from the case where DMA API is
used with IOMMU disabled.
Are you saying DMA API introduces overheads in this case?
Thanks
>
> >
> > > 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
> > > > >
> > > > > Thanks.
> > > > >
> > >
>
