linux-kernel - Re: [PATCH v5 3/7] cxl/region: Skip decoder reset on detach for autodiscovered regions

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Message-ID: <9c5150ba-c443-4ce1-a750-57736f0dabf0@amd.com>
Date: Mon, 26 Jan 2026 13:37:35 -0800
From: "Koralahalli Channabasappa, Smita" <skoralah@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>,
 Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
Cc: linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
 nvdimm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
 linux-pm@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>,
 Dan Williams <dan.j.williams@...el.com>,
 Yazen Ghannam <yazen.ghannam@....com>, Dave Jiang <dave.jiang@...el.com>,
 Davidlohr Bueso <dave@...olabs.net>, Matthew Wilcox <willy@...radead.org>,
 Jan Kara <jack@...e.cz>, "Rafael J . Wysocki" <rafael@...nel.org>,
 Len Brown <len.brown@...el.com>, Pavel Machek <pavel@...nel.org>,
 Li Ming <ming.li@...omail.com>, Jeff Johnson
 <jeff.johnson@....qualcomm.com>, Ying Huang <huang.ying.caritas@...il.com>,
 Yao Xingtao <yaoxt.fnst@...itsu.com>, Peter Zijlstra <peterz@...radead.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Nathan Fontenot <nathan.fontenot@....com>,
 Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
 Benjamin Cheatham <benjamin.cheatham@....com>,
 Zhijian Li <lizhijian@...itsu.com>, Borislav Petkov <bp@...en8.de>,
 Tomasz Wolski <tomasz.wolski@...itsu.com>
Subject: Re: [PATCH v5 3/7] cxl/region: Skip decoder reset on detach for
 autodiscovered regions

Hi Jonathan,

On 1/22/2026 8:18 AM, Jonathan Cameron wrote:
> On Thu, 22 Jan 2026 04:55:39 +0000
> Smita Koralahalli <Smita.KoralahalliChannabasappa@....com> wrote:
> 
>> __cxl_decoder_detach() currently resets decoder programming whenever a
>> region is detached if cxl_config_state is beyond CXL_CONFIG_ACTIVE. For
>> autodiscovered regions, this can incorrectly tear down decoder state
>> that may be relied upon by other consumers or by subsequent ownership
>> decisions.
>>
>> Skip cxl_region_decode_reset() during detach when CXL_REGION_F_AUTO is
>> set.
>>
>> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> purely on basis we should probably not undo things we didn't do in the
> first place.
> 
> J

Thank you!

I’m re reading Dan’s note here:
https://lore.kernel.org/all/6930dacd6510f_198110020@dwillia2-mobl4.notmuch/

Specifically this part:
"If the administrator actually wants to destroy and reclaim that
physical address space then they need to forcefully de-commit that
auto-assembled region via the @commit sysfs attribute. So that means
commit_store() needs to clear CXL_REGION_F_AUTO to get the decoder reset
to happen."

Today the sysfs commit=0 path inside commit_store() resets decoders 
without the AUTO check whereas the detach path now skips the reset when 
CXL_REGION_F_AUTO is set.

I think the same rationale should apply to the sysfs de-commit path as 
well? I’m trying to understand the implications of not guarding the 
reset with AUTO in commit_store().

Thanks
Smita