Re: [PATCH v9 31/37] hw/arm/smmuv3-accel: Add property to specify OAS bits

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Feb 02, 2026 at 03:38:50PM +0000, Shameer Kolothum Thodi wrote:

> > We can treat ATS as a per-PCIe device property.. I think it would be
> > fine to tell the SMMU that it always has ATS support, it will never do
> > anything with it unless it sees a PCIe device with an ATS cap, and the
> > physical STE generated by the hypervisor should sanitize the EATS.
> > 
> > BIOS overriding it should be reflected as the devices being reported
> > as not supporting ATS, qemu should have a per-device flag to disable
> > ATS.
> 
> Do we have way to detect that(IOMMU_FWSPEC_PCI_RC_ATS) from
> userspace now?

I don't think so.. I was describing how I suspect that should work.

The iommu driver is the only entity that decides if ATS should be
enabled per-device, so it should report back to userspace in iommufd
if the device is allowed to enable ATS or not. That should roll up any
FW overrides and the PCI cap block.

Jason