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

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Message-ID: <aSXbTe7lTbvzgwGe@aschofie-mobl2.lan>
Date: Tue, 25 Nov 2025 08:37:33 -0800
From: Alison Schofield <alison.schofield@...el.com>
To: Gregory Price <gourry@...rry.net>
CC: Robert Richter <rrichter@....com>, 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>, "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 Tue, Nov 25, 2025 at 08:54:58AM -0500, Gregory Price wrote:
> On Mon, Nov 24, 2025 at 07:26:51PM -0800, Alison Schofield wrote:
> > On Mon, Nov 24, 2025 at 03:10:07PM -0500, Gregory Price wrote:
> > > 
> > > IIRC the to_spa() function wouldn't be populated (will be NULL) if this
> > > is the case, so you wouldn't even be able to call the translation
> > > function.
> > 
> > The hpa_to_spa fn defined as a root decoder ops is an additional layer for
> > arch's needing HPA to SPA translation. It's optional. If there is no
> > hpa_to_spa fn, then it is assumed that the CXL HPA==SPA and that is the
> > 'final answer'  added to the trace log.
> > 
> > Sounds like you are on one of these systems, so maybe you could take a
> > look at what happens. If your devices support, try to inject and/or
> > clear poison and see the resulting kernel trace log. There is an
> > example for that here:
> > https://github.com/pmem/ndctl/blob/main/test/cxl-poison.sh
> > 
> 
> Servers am able to test on are @ 6.16 with cxl .17+.18 backports
> 
> I don't see: /sys/kernel/debug/cxl/$dev/${action}_poison
> in my sysfs
> 
> Have enabled enabling various debug and einj options.
> 
> When were these added? Am i missing build options?

Inject and clear poison are since 6.4.
Need CONFIG_DEBUG_FS, but of course you wouldn't have even seen the
the /sys/kernel/debug path if that were missing.

Could be your devices don't support inject or clear. At init time we set
the bits inidicating what poison opcodes the device supports, see
cxl_set_poison_cmd_enabled().
50d527f52cbf ("cxl/mem: Add debugfs attributes for poison inject and clear")

Devices may support list but not inject and clear. Look for this attribute:
/sys/bus/cxl/devices/memX/trigger_poison_list. If that is present, then a
quicker, maybe fruitful check, may be 'cxl list -M --media-errors'. If you're
lucky ;) your devices come pre-loaded with poison. That cmd will emit the
poisoned DPAs and if part of a region, the SPAs too. cxl-list is getting that
all from the kernel trace log, so if you don't have 'cxl list', just trigger
directly and examine the trace log.

-- Alison

> 
> ~Gregory