Re: [PATCH v4 12/18] iommu/vt-d: Handle reattach of the restored domain

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Aug 28, 2026 at 09:55:18AM +0800, Baolu Lu wrote:
> That looks reasonable to me. I have no concerns about keeping ATS
> enabled on preserved devices across kexec reboot, as long as the
> software state is synchronized in the new kernel.

The new kernel should issue an ATC flush when it changes away from the
inherented domain.

> By the way, is disabling ATS an option? 

No, many devices require ATS.

It is not that ATS and PRI are coupled, there are good reasons to do
ATS to pinned memory too.

PRI is a PITA, I continue to think PRI through the iommu was a
mistake. Devices that have device-specific PRI handling are fine
because that all lives in the VM. Devices relying on SMMU PRI
forwarding must also somehow not loose any PRI events across the kexec
and must ultimately inject all of them into the VM.

> The current design already requires disabling PCI/PRI during kexec,
> right? 

That is also not OK, but there certainly is a useful universe of VMs
that might pretend to use PRI but actually only use device specific
fault delivery.

So ignoring PRI for the moment is possibly OK. Someone using this
should understand what VM shapes thay are making and if that
limitation is OK.

Jason