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, 121 insertions, 0 deletions

diff --git a/drivers/dma/idxd/compat.c b/drivers/dma/idxd/compat.c
new file mode 100644
index 000000000..95b8ef958
--- /dev/null
+++ b/drivers/dma/idxd/compat.c
@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright(c) 2021 Intel Corporation. All rights rsvd. */
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/device/bus.h>
+#include "idxd.h"
+
+extern void device_driver_detach(struct device *dev);
+
+#define DRIVER_ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store)	\
+	struct driver_attribute driver_attr_##_name =		\
+	__ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store)
+
+static ssize_t unbind_store(struct device_driver *drv, const char *buf, size_t count)
+{
+	const struct bus_type *bus = drv->bus;
+	struct device *dev;
+	int rc = -ENODEV;
+
+	dev = bus_find_device_by_name(bus, NULL, buf);
+	if (!dev)
+		return -ENODEV;
+
+	if (dev->driver) {
+		device_driver_detach(dev);
+		rc = count;
+	}
+
+	put_device(dev);
+
+	return rc;
+}
+static DRIVER_ATTR_IGNORE_LOCKDEP(unbind, 0200, NULL, unbind_store);
+
+static ssize_t bind_store(struct device_driver *drv, const char *buf, size_t count)
+{
+	const struct bus_type *bus = drv->bus;
+	struct device *dev;
+	struct device_driver *alt_drv = NULL;
+	int rc = -ENODEV;
+	struct idxd_dev *idxd_dev;
+
+	dev = bus_find_device_by_name(bus, NULL, buf);
+	if (!dev)
+		return -ENODEV;
+
+	if (dev->driver || drv != &dsa_drv.drv)
+		goto err_put_dev;
+
+	idxd_dev = confdev_to_idxd_dev(dev);
+	if (is_idxd_dev(idxd_dev)) {
+		alt_drv = driver_find("idxd", bus);
+	} else if (is_idxd_wq_dev(idxd_dev)) {
+		struct idxd_wq *wq = confdev_to_wq(dev);
+
+		if (is_idxd_wq_kernel(wq))
+			alt_drv = driver_find("dmaengine", bus);
+		else if (is_idxd_wq_user(wq))
+			alt_drv = driver_find("user", bus);
+	}
+	if (!alt_drv)
+		goto err_put_dev;
+
+	rc = device_driver_attach(alt_drv, dev);
+	if (rc < 0)
+		goto err_put_dev;
+
+	put_device(dev);
+
+	return count;
+
+err_put_dev:
+	put_device(dev);
+
+	return rc;
+}
+static DRIVER_ATTR_IGNORE_LOCKDEP(bind, 0200, NULL, bind_store);
+
+static struct attribute *dsa_drv_compat_attrs[] = {
+	&driver_attr_bind.attr,
+	&driver_attr_unbind.attr,
+	NULL,
+};
+
+static const struct attribute_group dsa_drv_compat_attr_group = {
+	.attrs = dsa_drv_compat_attrs,
+};
+
+static const struct attribute_group *dsa_drv_compat_groups[] = {
+	&dsa_drv_compat_attr_group,
+	NULL,
+};
+
+static int idxd_dsa_drv_probe(struct idxd_dev *idxd_dev)
+{
+	return -ENODEV;
+}
+
+static void idxd_dsa_drv_remove(struct idxd_dev *idxd_dev)
+{
+}
+
+static enum idxd_dev_type dev_types[] = {
+	IDXD_DEV_NONE,
+};
+
+struct idxd_device_driver dsa_drv = {
+	.name = "dsa",
+	.probe = idxd_dsa_drv_probe,
+	.remove = idxd_dsa_drv_remove,
+	.type = dev_types,
+	.drv = {
+		.suppress_bind_attrs = true,
+		.groups = dsa_drv_compat_groups,
+	},
+};
+
+module_idxd_driver(dsa_drv);
+MODULE_IMPORT_NS("IDXD");