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

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Message-ID: <aWcUiRJpUesoJL3G@aschofie-mobl2.lan>
Date: Tue, 13 Jan 2026 19:59:05 -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 v9 13/13] cxl: Disable HPA/SPA translation handlers for
 Normalized Addressing

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.)