x86/amd_node: Fix PCI device reference counting in amd_smn_init()grafted

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com

1 files changed, 103 insertions, 0 deletions

diff --git a/drivers/dax/hmem/device.c b/drivers/dax/hmem/device.c
new file mode 100644
index 000000000..d70359b43
--- /dev/null
+++ b/drivers/dax/hmem/device.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/platform_device.h>
+#include <linux/memregion.h>
+#include <linux/module.h>
+#include <linux/dax.h>
+#include <linux/mm.h>
+#include "../bus.h"
+
+static bool nohmem;
+module_param_named(disable, nohmem, bool, 0444);
+
+static bool platform_initialized;
+static DEFINE_MUTEX(hmem_resource_lock);
+static struct resource hmem_active = {
+	.name = "HMEM devices",
+	.start = 0,
+	.end = -1,
+	.flags = IORESOURCE_MEM,
+};
+
+int walk_hmem_resources(struct device *host, walk_hmem_fn fn)
+{
+	struct resource *res;
+	int rc = 0;
+
+	mutex_lock(&hmem_resource_lock);
+	for (res = hmem_active.child; res; res = res->sibling) {
+		rc = fn(host, (int) res->desc, res);
+		if (rc)
+			break;
+	}
+	mutex_unlock(&hmem_resource_lock);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(walk_hmem_resources);
+
+static void hmem_work(struct work_struct *work)
+{
+	/* place holder until dax_hmem driver attaches */
+}
+
+static struct hmem_platform_device hmem_platform = {
+	.pdev = {
+		.name = "hmem_platform",
+		.id = 0,
+	},
+	.work = __WORK_INITIALIZER(hmem_platform.work, hmem_work),
+};
+
+static void __hmem_register_resource(int target_nid, struct resource *res)
+{
+	struct resource *new;
+	int rc;
+
+	new = __request_region(&hmem_active, res->start, resource_size(res), "",
+			       0);
+	if (!new) {
+		pr_debug("hmem range %pr already active\n", res);
+		return;
+	}
+
+	new->desc = target_nid;
+
+	if (platform_initialized)
+		return;
+
+	rc = platform_device_register(&hmem_platform.pdev);
+	if (rc) {
+		pr_err_once("failed to register device-dax hmem_platform device\n");
+		return;
+	}
+
+	platform_initialized = true;
+}
+
+void hmem_register_resource(int target_nid, struct resource *res)
+{
+	if (nohmem)
+		return;
+
+	mutex_lock(&hmem_resource_lock);
+	__hmem_register_resource(target_nid, res);
+	mutex_unlock(&hmem_resource_lock);
+}
+
+static __init int hmem_register_one(struct resource *res, void *data)
+{
+	hmem_register_resource(phys_to_target_node(res->start), res);
+
+	return 0;
+}
+
+static __init int hmem_init(void)
+{
+	walk_soft_reserve_res(0, -1, NULL, hmem_register_one);
+	return 0;
+}
+
+/*
+ * As this is a fallback for address ranges unclaimed by the ACPI HMAT
+ * parsing it must be at an initcall level greater than hmat_init().
+ */
+device_initcall(hmem_init);