linux-kernel - [PATCH v4 6/9] cxl/region: Add register

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Message-ID: <20251120031925.87762-7-Smita.KoralahalliChannabasappa@amd.com>
Date: Thu, 20 Nov 2025 03:19:22 +0000
From: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-fsdevel@...r.kernel.org>,
	<linux-pm@...r.kernel.org>
CC: 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>, Jonathan Cameron <jonathan.cameron@...wei.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 KH <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>, Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH v4 6/9] cxl/region: Add register_dax flag to defer DAX setup

Stop creating cxl_dax during cxl_region_probe(). Early DAX registration
can online memory before ownership of Soft Reserved ranges is finalized.
This makes it difficult to tear down regions later when HMEM determines
that a region should not claim that range.

Introduce a register_dax flag in struct cxl_region_params and gate DAX
registration on this flag. Leave probe time registration disabled for
regions discovered during early CXL enumeration; set the flag only for
regions created dynamically at runtime to preserve existing behaviour.

This patch prepares the region code for later changes where cxl_dax
setup occurs from the HMEM path only after ownership arbitration
completes.

Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
---
 drivers/cxl/core/region.c | 21 ++++++++++++++++-----
 drivers/cxl/cxl.h         |  1 +
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 94dbbd6b5513..c17cd8706b9d 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -2540,9 +2540,11 @@ static int cxl_region_calculate_adistance(struct notifier_block *nb,
 static struct cxl_region *devm_cxl_add_region(struct cxl_root_decoder *cxlrd,
 					      int id,
 					      enum cxl_partition_mode mode,
-					      enum cxl_decoder_type type)
+					      enum cxl_decoder_type type,
+					      bool register_dax)
 {
 	struct cxl_port *port = to_cxl_port(cxlrd->cxlsd.cxld.dev.parent);
+	struct cxl_region_params *p;
 	struct cxl_region *cxlr;
 	struct device *dev;
 	int rc;
@@ -2553,6 +2555,9 @@ static struct cxl_region *devm_cxl_add_region(struct cxl_root_decoder *cxlrd,
 	cxlr->mode = mode;
 	cxlr->type = type;
 
+	p = &cxlr->params;
+	p->register_dax = register_dax;
+
 	dev = &cxlr->dev;
 	rc = dev_set_name(dev, "region%d", id);
 	if (rc)
@@ -2593,7 +2598,8 @@ static ssize_t create_ram_region_show(struct device *dev,
 }
 
 static struct cxl_region *__create_region(struct cxl_root_decoder *cxlrd,
-					  enum cxl_partition_mode mode, int id)
+					  enum cxl_partition_mode mode, int id,
+					  bool register_dax)
 {
 	int rc;
 
@@ -2615,7 +2621,8 @@ static struct cxl_region *__create_region(struct cxl_root_decoder *cxlrd,
 		return ERR_PTR(-EBUSY);
 	}
 
-	return devm_cxl_add_region(cxlrd, id, mode, CXL_DECODER_HOSTONLYMEM);
+	return devm_cxl_add_region(cxlrd, id, mode, CXL_DECODER_HOSTONLYMEM,
+				   register_dax);
 }
 
 static ssize_t create_region_store(struct device *dev, const char *buf,
@@ -2629,7 +2636,7 @@ static ssize_t create_region_store(struct device *dev, const char *buf,
 	if (rc != 1)
 		return -EINVAL;
 
-	cxlr = __create_region(cxlrd, mode, id);
+	cxlr = __create_region(cxlrd, mode, id, true);
 	if (IS_ERR(cxlr))
 		return PTR_ERR(cxlr);
 
@@ -3523,7 +3530,7 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
 
 	do {
 		cxlr = __create_region(cxlrd, cxlds->part[part].mode,
-				       atomic_read(&cxlrd->region_id));
+				       atomic_read(&cxlrd->region_id), false);
 	} while (IS_ERR(cxlr) && PTR_ERR(cxlr) == -EBUSY);
 
 	if (IS_ERR(cxlr)) {
@@ -3930,6 +3937,10 @@ static int cxl_region_probe(struct device *dev)
 					p->res->start, p->res->end, cxlr,
 					is_system_ram) > 0)
 			return 0;
+
+		if (!p->register_dax)
+			return 0;
+
 		return devm_cxl_add_dax_region(cxlr);
 	default:
 		dev_dbg(&cxlr->dev, "unsupported region mode: %d\n",
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index af78c9fd37f2..324220596890 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -495,6 +495,7 @@ struct cxl_region_params {
 	struct cxl_endpoint_decoder *targets[CXL_DECODER_MAX_INTERLEAVE];
 	int nr_targets;
 	resource_size_t cache_size;
+	bool register_dax;
 };
 
 enum cxl_partition_mode {
-- 
2.17.1