linux-kernel - Re: [PATCH 0/6] dax/hmem, cxl: Coordinate Soft Reserved handling with CXL

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Message-ID: <aK5BY7bQ_dMZLFNT@aschofie-mobl2.lan>
Date: Tue, 26 Aug 2025 16:21:07 -0700
From: Alison Schofield <alison.schofield@...el.com>
To: 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>, Davidlohr Bueso <dave@...olabs.net>, "Jonathan
 Cameron" <jonathan.cameron@...wei.com>, Dave Jiang <dave.jiang@...el.com>,
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	PradeepVineshReddy Kodamati <PradeepVineshReddy.Kodamati@....com>, Zhijian Li
	<lizhijian@...itsu.com>
Subject: Re: [PATCH 0/6] dax/hmem, cxl: Coordinate Soft Reserved handling
 with CXL

On Fri, Aug 22, 2025 at 03:41:56AM +0000, Smita Koralahalli wrote:
> This series aims to address long-standing conflicts between dax_hmem and
> CXL when handling Soft Reserved memory ranges.

Hi Smita,

I was able to try this out today and it looks good. See one question
about the !CXL_REGION case below.

Test case of a hot replace a dax region worked as expected. It appeared
with no soft reserved and after tear down, the same region could be
rebuilt in place.

Test case with CONFIG_CXL_REGION=N looks good too, as in DAX consumed
the entire resource. Do we intend the Soft Reserved resource to remain
like this:
c080000000-17dbfffffff : CXL Window 0
  c080000000-c47fffffff : Soft Reserved
    c080000000-c47fffffff : dax2.0
      c080000000-c47fffffff : System RAM (kmem)

These other issues noted previously did not re-appear:
- kmem dax3.0: probe with driver kmem failed with error -16
- resource: Unaddressable device  [ ] conflicts with []

-- Alison

snip