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

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Message-ID: <aTEMeRzI0_zcT-S3@aschofie-mobl2.lan>
Date: Wed, 3 Dec 2025 20:22:17 -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.

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.

-- Alison


> 
> Thanks,
> 
> -Robert