Re: [PATCH v6 5/5] vfio/type1: Use mdev bus iommu_ops for IOMMU callbacks

[Lu Baolu]

Hi Alex,

On 11/3/20 1:22 PM, Lu Baolu wrote:
> Hi Alex,
>
> On 10/31/20 5:06 AM, Alex Williamson wrote:
> > On Fri, 30 Oct 2020 06:16:28 +0000
> > "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
> >
> > > > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > > > Sent: Friday, October 30, 2020 12:58 PM
> > > >
> > > > With the IOMMU driver registering iommu_ops for the mdev_bus, the
> > > > IOMMU
> > > > operations on an mdev could be done in the same way as any normal 
> > > > device
> > > > (for example, PCI/PCIe). There's no need to distinguish an mdev from
> > > > others for iommu operations. Remove the unnecessary code.
> > >
> > > This is really a nice cleanup as the output of this change! :)
> >
> > It's easy to remove a bunch of code when the result is breaking
> > everyone else.  Please share with me how SR-IOV backed mdevs continue
> > to work on AMD platforms, or how they might work on ARM platforms, when
> > siov_iommu_ops (VT-d only) becomes the one and only provider of
> > iommu_ops on the mdev bus.  Hard NAK on this series.  Thanks,
>
> I focused too much on a feature and forgot about university. I should
> apologize for this. Sorry about it!
>
> Back to the original intention of this series. The aux domain was
> allocated in vfio/mdev, but it's also needed by the vDCM component of a
> device driver for mediated callbacks. Currently vfio/mdev or iommu core
> has no support for this.
>
> We had a proposal when we first did aux-domain support. But was not
> discussed since there was no consumer at that time.
>
> https://lore.kernel.org/linux-iommu/20181105073408.21815-7-baolu.lu@xxxxxxxxxxxxxxx/ 

Exposing iommu_domain outside of the vfio/iommu abstract seems not a
secure idea. I have posted a new proposal. Can you please help to
review?

https://lore.kernel.org/linux-iommu/20201112022407.2063896-1-baolu.lu@xxxxxxxxxxxxxxx/

Best regards.
baolu

> Does it look good to you? I can send patches of such solution for
> discussion if you think it's a right way.
>
> Extending the iommu core for subdevice passthrough support sounds an
> interesting topic, but it will take much time before we reach a
> consensus. It sounds a good topic for the next year's LPC/MC :-).
>
> Best regards,
> baolu