linux-kernel - Re: [PATCH v9 13/13] cxl: Disable HPA/SPA translation handlers for Normalized Addressing

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Message-ID: <aWd-08OYXJBCR0Oz@rric.localdomain>
Date: Wed, 14 Jan 2026 12:32:35 +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 v9 13/13] cxl: Disable HPA/SPA translation handlers for
 Normalized Addressing

On 13.01.26 19:59:05, Alison Schofield wrote:
> On Sat, Jan 10, 2026 at 12:46:58PM +0100, Robert Richter wrote:
> > The root decoder provides the callbacks hpa_to_spa and spa_to_hpa to
> > perform Host Physical Address (HPA) and System Physical Address
> > translations, respectively. The callbacks are required to convert
> > addresses when HPA != SPA. XOR interleaving depends on this mechanism,
> > and the necessary handlers are implemented.
> > 
> > The translation handlers are used for poison injection
> > (trace_cxl_poison, cxl_poison_inject_fops) and error handling
> > (cxl_event_trace_record).
> > 
> > In AMD Zen5 systems with Normalized Addressing, endpoint addresses are
> > not SPAs, and translation handlers are required for these features to
> > function correctly.
> > 
> > Now, as ACPI PRM translation could be expensive in tracing or error
> > handling code paths, do not yet enable translations to avoid its
> > intensive use. Instead, disable those features which are used only for
> > debugging and enhanced logging.
> > 
> > Introduce the flag CXL_REGION_F_NORM_ADDR that indicates Normalized
> > Addressing for a region and use it to disable poison injection and DPA
> > to HPA conversion.
> > 
> > Note: Dropped unused CXL_DECODER_F_MASK macro.
> 
> Reviewed-by: Alison Schofield <alison.schofield@...el.com>
> 
> So not for the commit log, but for my closure ;) - 
> 
> A system with normalized addressing:
> 
> will still:
> 	support poison listings by memdev and by region
> 	support poison inject and clear by memdev
> 
> they'll be different, in that:
> 	if a DPA address maps into a region, the region SPA mapping will
> 	always be ULLONG_MAX. The region name will still be available and
> 	valid. That same difference applies for General Media and DRAM events.
> 	(This is the 'enhanced logging' referred to in the commit log.)
> 
> will not:
> 	support poison inject or clear by region.
> 	(This is the 'debugging' referred to in commit log.)
> 

Good conclusion. :-) Thanks for review.

-Robert