Re: [PATCH v3 24/30] vfio-pci/zdev: wire up group notifier

Jason Gunthorpe
2022-02-08T22:23:17Z

On Tue, Feb 08, 2022 at 03:33:58PM -0500, Matthew Rosato wrote:

> > Is the purpose of IOAT to associate the device to a set of KVM page
> > tables? That seems like a container or future iommufd operation. I
>
> Yes, here we are establishing a relationship with the DMA table in the guest
> so that once mappings are established guest PCI operations (handled via
> special instructions in s390) don't need to go through the host but can be
> directly handled by firmware (so, effectively guest can keep running on its
> vcpu vs breaking out).

Oh, well, certainly sounds like a NAK on that - anything to do with
the DMA translation of a PCI device must go through the iommu layer,
not here.

Lets not repeat the iommu subsytem bypass mess power made please.

> It's more that non-KVM userspace doesn't care about what these ioctls are
> doing... The enabling of 'interp, aif, ioat' is only pertinent when there
> is a KVM userspace, specifically because the information being shared /
> actions being performed as a result are only relevant to properly enabling
> zPCI features when the zPCI device is being passed through to a VM
> guest.

Then why are they KVM ioctls?

Jason