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

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Message-ID: <aSOxXX7xX4jYqqvF@aschofie-mobl2.lan>
Date: Sun, 23 Nov 2025 17:14:05 -0800
From: Alison Schofield <alison.schofield@...el.com>
To: Robert Richter <rrichter@....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 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.

If address translations are not supported/supportable, a quick exit
on any attempt (DPA->SPA or SPA->DPA) with this config seems needed. 

Better to fail and report ULLONG_MAX than leave open the possibility
of adding the wrong address to trace events or using the wrong address
in poison by region offset action.

Maybe you already know that it fails gracefully? If so, then it comes
down to documenting the limitation.

-- Alison


> 
> Thanks,
> 
> -Robert