Re: [PATCH v9 10/13] cxl: Enable AMD Zen5 address translation using ACPI PRMT

[Ard Biesheuvel]

On Wed, 14 Jan 2026 at 15:00, Robert Richter <rrichter@xxxxxxx> wrote:
>
> On Wed, Jan 14, 2026 at 08:47:22AM +0100, Ard Biesheuvel wrote:
> > (cc Peter)
> >
> > On Sat, 10 Jan 2026 at 12:46, Robert Richter <rrichter@xxxxxxx> wrote:
> > >
> > > Add AMD Zen5 support for address translation.
> > >
> > ...
> > > Do the following to implement AMD Zen5 address translation:
> > >
> > > Introduce a new file core/atl.c to handle ACPI PRM specific address
> > > translation code. Naming is loosely related to the kernel's AMD
> > > Address Translation Library (CONFIG_AMD_ATL) but implementation does
> > > not depend on it, nor it is vendor specific. Use Kbuild and Kconfig
> > > options respectively to enable the code depending on architecture and
> > > platform options.
> > >
> > > AMD Zen5 systems support the ACPI PRM CXL Address Translation firmware
> > > call (see ACPI v6.5 Porting Guide, Address Translation - CXL DPA to
> > > System Physical Address). Firmware enables the PRM handler if the
> > > platform has address translation implemented. Check firmware and
> > > kernel support of ACPI PRM using the specific GUID. On success enable
> > > address translation by setting up the earlier introduced root port
> > > callback, see function cxl_prm_setup_translation(). Setup is done in
> > > cxl_setup_prm_address_translation(), it is the only function that
> > > needs to be exported. For low level PRM firmware calls, use the ACPI
> > > framework.
> > >
> >
> > Does the PRM service in question tolerate being invoked unprivileged?
> > The PRM spec requires this, and this is something we may need to
> > enforce at some point.
> >
> > cc'ing Peter with whom I've discussed this just recently.
>
> Interesting appoach, need to check if that works. I haven't tried that
> yet. Though, that needs some rework of the kernel code as some high
> priority code depends on the translation and that would cause kind of
> priority inversion. E.g. an interrupt handler cannot wait until a
> dpa-to-spa conversion is done.
>

This is not about running it in user space, but about running the code
in an unprivileged sandbox. So scheduling wpuldn't really come into
play here.

> For CXL it is only used for region setup in the init path and process
> context. For tracing and error handling those translations are
> disabled. See patch 13/13.
>