linux-kernel - [RFC PATCH 8/9] drivers/cxl: add protected

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Message-ID: <20251107224956.477056-9-gourry@gourry.net>
Date: Fri,  7 Nov 2025 17:49:53 -0500
From: Gregory Price <gourry@...rry.net>
To: linux-mm@...ck.org
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Subject: [RFC PATCH 8/9] drivers/cxl: add protected_memory bit to cxl region

Add protected_memory bit to cxl region.  The setting is subsequently
forwarded to the dax device it creates. This allows the auto-hotplug
process to occur without an intermediate step requiring udev to poke
the DAX device protected memory bit explicitly before onlining.

Signed-off-by: Gregory Price <gourry@...rry.net>
---
 drivers/cxl/core/region.c | 30 ++++++++++++++++++++++++++++++
 drivers/cxl/cxl.h         |  2 ++
 drivers/dax/cxl.c         |  1 +
 3 files changed, 33 insertions(+)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index b06fee1978ba..a0e28821961c 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -754,6 +754,35 @@ static ssize_t size_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RW(size);
 
+static ssize_t protected_memory_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	struct cxl_region *cxlr = to_cxl_region(dev);
+
+	return sysfs_emit(buf, "%d\n", cxlr->protected_memory);
+}
+
+static ssize_t protected_memory_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t len)
+{
+	struct cxl_region *cxlr = to_cxl_region(dev);
+	bool val;
+	int rc;
+
+	rc = kstrtobool(buf, &val);
+	if (rc)
+		return rc;
+
+	ACQUIRE(rwsem_write_kill, rwsem)(&cxl_rwsem.region);
+	if ((rc = ACQUIRE_ERR(rwsem_read_intr, &rwsem)))
+		return rc;
+
+	cxlr->protected_memory = val;
+	return len;
+}
+static DEVICE_ATTR_RW(protected_memory);
+
 static struct attribute *cxl_region_attrs[] = {
 	&dev_attr_uuid.attr,
 	&dev_attr_commit.attr,
@@ -762,6 +791,7 @@ static struct attribute *cxl_region_attrs[] = {
 	&dev_attr_resource.attr,
 	&dev_attr_size.attr,
 	&dev_attr_mode.attr,
+	&dev_attr_protected_memory.attr,
 	NULL,
 };
 
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 231ddccf8977..0ff4898224ba 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -530,6 +530,7 @@ enum cxl_partition_mode {
  * @coord: QoS access coordinates for the region
  * @node_notifier: notifier for setting the access coordinates to node
  * @adist_notifier: notifier for calculating the abstract distance of node
+ * @protected_memory: mark region memory as protected from kernel allocation
  */
 struct cxl_region {
 	struct device dev;
@@ -543,6 +544,7 @@ struct cxl_region {
 	struct access_coordinate coord[ACCESS_COORDINATE_MAX];
 	struct notifier_block node_notifier;
 	struct notifier_block adist_notifier;
+	bool protected_memory;
 };
 
 struct cxl_nvdimm_bridge {
diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
index 13cd94d32ff7..a4232a5507b5 100644
--- a/drivers/dax/cxl.c
+++ b/drivers/dax/cxl.c
@@ -27,6 +27,7 @@ static int cxl_dax_region_probe(struct device *dev)
 		.id = -1,
 		.size = range_len(&cxlr_dax->hpa_range),
 		.memmap_on_memory = true,
+		.protected_memory = cxlr->protected_memory,
 	};
 
 	return PTR_ERR_OR_ZERO(devm_create_dev_dax(&data));
-- 
2.51.1