linux-kernel - Re: [PATCH v6 00/11] cxl: ACPI PRM Address Translation Support and AMD Zen5 enablement

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Message-ID: <aTKttv6plTq0xTsA@rric.localdomain>
Date: Fri, 5 Dec 2025 11:02:30 +0100
From: Robert Richter <rrichter@....com>
To: Alison Schofield <alison.schofield@...el.com>
Cc: Vishal Verma <vishal.l.verma@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org, Gregory Price <gourry@...rry.net>,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
	Terry Bowman <terry.bowman@....com>,
	Joshua Hahn <joshua.hahnjy@...il.com>
Subject: Re: [PATCH v6 00/11] cxl: ACPI PRM Address Translation Support and
 AMD Zen5 enablement

On 03.12.25 20:22:17, Alison Schofield wrote:
> On Mon, Nov 17, 2025 at 03:58:40PM +0100, Robert Richter wrote:
> > On 14.11.25 12:01:29, Alison Schofield wrote:
> > 
> > > Does this work 'as is', no changes required, to support DPA->SPA
> > > (used in CXL Events) or SPA->DPA (used in poison by region offset)?
> > 
> > The PRM handler could be used for to-SPA translations, but it might
> > not fit well to other users such as profiling, tracing and error
> > handling. Those users are executing in a critical path from a
> > performance or stability point of view. Performing a firmware call
> > could cause problems here. Since the to-DPA translation is missing
> > too, a different approach to solve address translation might work
> > better, such as examining the region parameters. The kernel's address
> > translation library could possibly be extended and used too. That
> > needs to be figured out. Also, my main focus for the patches is region
> > enablement.
> 
> I see a dpa-to-spa prm routine. I don't know enough about the cost of
> using it to say it's not worth using for CXl trace events that want
> to report a SPA (from a DPA).
> 
> If we cannot trust what the address translation code will emit in
> this case, forcing it to ULLONG_MAX would be safest.

I will implement those handlers accordingly. Thanks Alison.

-Robert