Re: [PATCH RFCv1 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices

Nicolin Chen
2026-02-03T19:24:55Z

On Tue, Feb 03, 2026 at 06:59:35PM +0000, Robin Murphy wrote:
> On 2026-02-03 5:55 pm, Jason Gunthorpe wrote:
> > On Tue, Feb 03, 2026 at 09:45:17AM -0800, Nicolin Chen wrote:
> > > Btw, attaching to IOMMU_DOMAIN_BLOCKED/group->blocking_domain is not
> > > allowed in general if require_direct=true. I assume this case can be
> > > an exception since there's no point in allowing a device that has no
> > > driver yet to access any reserved region?
>
> No, the point of RMRs in general is that the device can be assumed to
> already be accessing them, and that access must be preserved, regardless of
> whether an OS driver may or may not take over the device later.

I see. Thanks for the input.

> In fact RMRs
> with the "Remapping Permitted" flag are only strictly needed *until* an OS
> driver has taken control over whatever it was that firmware left them doing.

Yes. I see that doesn't set require_direct.

Nicolin