linux-kernel - [PATCH v5 7/7] dax/hmem: Preserve fallback SOFT RESERVED regions if DAX HMEM loads late

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Message-ID: <20250715180407.47426-8-Smita.KoralahalliChannabasappa@amd.com>
Date: Tue, 15 Jul 2025 18:04:07 +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: Davidlohr Bueso <dave@...olabs.net>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, Dave Jiang <dave.jiang@...el.com>, "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>, 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>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>, Terry Bowman
	<terry.bowman@....com>, Robert Richter <rrichter@....com>, Benjamin Cheatham
	<benjamin.cheatham@....com>, PradeepVineshReddy Kodamati
	<PradeepVineshReddy.Kodamati@....com>, Zhijian Li <lizhijian@...itsu.com>
Subject: [PATCH v5 7/7] dax/hmem: Preserve fallback SOFT RESERVED regions if DAX HMEM loads late

After CXL completes trimming SOFT RESERVED ranges that intersect with CXL
regions, it invokes hmem_fallback_register_device() to register any
leftover ranges. If this occurs before the DAX HMEM driver has
initialized, the call becomes a no-op and those resources are lost.

To prevent this, store fallback-registered resources in a separate
deferred tree (hmem_deferred_active). When the DAX HMEM driver is
initialized, it walks this deferred list to properly register DAX
devices.

Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
---
 drivers/dax/hmem/device.c      | 17 +++++++++++++----
 drivers/dax/hmem/hmem.c        |  1 -
 drivers/dax/hmem/hmem_notify.c |  2 ++
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/dax/hmem/device.c b/drivers/dax/hmem/device.c
index cc1ed7bbdb1a..41c5886a30d1 100644
--- a/drivers/dax/hmem/device.c
+++ b/drivers/dax/hmem/device.c
@@ -16,13 +16,21 @@ static struct resource hmem_active = {
 	.flags = IORESOURCE_MEM,
 };
 
+static struct resource hmem_deferred_active = {
+	.name = "Deferred HMEM devices",
+	.start = 0,
+	.end = -1,
+	.flags = IORESOURCE_MEM,
+};
+static struct resource *hmem_resource_root = &hmem_active;
+
 int walk_hmem_resources(walk_hmem_fn fn)
 {
 	struct resource *res;
 	int rc = 0;
 
 	mutex_lock(&hmem_resource_lock);
-	for (res = hmem_active.child; res; res = res->sibling) {
+	for (res = hmem_resource_root->child; res; res = res->sibling) {
 		rc = fn((int) res->desc, res);
 		if (rc)
 			break;
@@ -36,8 +44,8 @@ static void __hmem_register_resource(int target_nid, struct resource *res)
 {
 	struct resource *new;
 
-	new = __request_region(&hmem_active, res->start, resource_size(res), "",
-			       0);
+	new = __request_region(hmem_resource_root, res->start,
+			       resource_size(res), "", 0);
 	if (!new) {
 		pr_debug("hmem range %pr already active\n", res);
 		return;
@@ -72,7 +80,8 @@ static __init int hmem_init(void)
 		walk_iomem_res_desc(IORES_DESC_SOFT_RESERVED,
 				    IORESOURCE_MEM, 0, -1, NULL,
 				    hmem_register_one);
-	}
+	} else
+		hmem_resource_root = &hmem_deferred_active;
 
 	pdev = platform_device_alloc("hmem_platform", 0);
 	if (!pdev) {
diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
index 16873ae0a53b..76a381c274a8 100644
--- a/drivers/dax/hmem/hmem.c
+++ b/drivers/dax/hmem/hmem.c
@@ -131,7 +131,6 @@ static int dax_hmem_platform_probe(struct platform_device *pdev)
 
 	if (IS_ENABLED(CONFIG_CXL_ACPI)) {
 		hmem_register_fallback_handler(hmem_register_device);
-		return 0;
 	}
 
 	return walk_hmem_resources(hmem_register_device);
diff --git a/drivers/dax/hmem/hmem_notify.c b/drivers/dax/hmem/hmem_notify.c
index 1b366ffbda66..6c276c5bd51d 100644
--- a/drivers/dax/hmem/hmem_notify.c
+++ b/drivers/dax/hmem/hmem_notify.c
@@ -23,5 +23,7 @@ void hmem_fallback_register_device(int target_nid, const struct resource *res)
 
 	if (hmem_fn)
 		hmem_fn(target_nid, res);
+	else
+		hmem_register_resource(target_nid, (struct resource *)res);
 }
 EXPORT_SYMBOL_GPL(hmem_fallback_register_device);
-- 
2.17.1