[PATCH 3/3] platform/x86/intel/tpmi/plr: Prevent fault during unbind

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

This driver faults when intel vsec driver unbound from PCI driver
interface. For example:

echo 0000:00:03.1 > /sys/bus/pci/drivers/intel_vsec/unbind

This is caused by accessing plr->dbgfs_dir after vsec_tpmi driver is
removed. Here vsec_tpmi driver is the parent. On unbind, the parent
device remove callback is called first which here will remove debugfs
interface. Hence plr->dbgfs_dir is no longer valid.

Register notifier for TPMI_CORE_EXIT and make this pointer to NULL,
so that debugfs_remove_recursive() is not called with bad plr->dbgfs_dir
pointer.

After notifier is returned the vsec_tpmi driver will call remove debugfs
by calling debugfs_remove_recursive().

Fixes: 811f67c51636 ("platform/x86/intel/tpmi: Add new auxiliary driver for performance limits")
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: <Stable@vger.kernel.org>
---
 drivers/platform/x86/intel/plr_tpmi.c | 43 +++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/intel/plr_tpmi.c b/drivers/platform/x86/intel/plr_tpmi.c
index 05727169f49c..644df673896b 100644
--- a/drivers/platform/x86/intel/plr_tpmi.c
+++ b/drivers/platform/x86/intel/plr_tpmi.c
@@ -22,6 +22,7 @@
 #include <linux/module.h>
 #include <linux/mod_devicetable.h>
 #include <linux/mutex.h>
+#include <linux/notifier.h>
 #include <linux/seq_file.h>
 #include <linux/sprintf.h>
 #include <linux/types.h>
@@ -60,6 +61,8 @@ struct tpmi_plr {
 	struct tpmi_plr_die *die_info;
 	int num_dies;
 	struct auxiliary_device *auxdev;
+	struct notifier_block nb;
+	struct mutex lock; /* Protect access to dbgfs_dir  */
 };
 
 static const char * const plr_coarse_reasons[] = {
@@ -255,6 +258,30 @@ static ssize_t plr_status_write(struct file *filp, const char __user *ubuf,
 }
 DEFINE_SHOW_STORE_ATTRIBUTE(plr_status);
 
+static int intel_plr_notify(struct notifier_block *self, unsigned long action, void *data)
+{
+	struct tpmi_plr *plr = container_of(self, struct tpmi_plr, nb);
+
+	if (action == TPMI_CORE_EXIT) {
+		guard(mutex)(&plr->lock);
+		plr->dbgfs_dir = NULL;
+	}
+
+	return NOTIFY_DONE;
+}
+
+static int intel_plr_register_notifier(struct notifier_block *nb)
+{
+	nb->notifier_call = intel_plr_notify;
+	nb->priority = 0;
+	return tpmi_register_notifier(nb);
+}
+
+static void intel_plr_unregister_notifier(struct notifier_block *nb)
+{
+	tpmi_unregister_notifier(nb);
+}
+
 static int intel_plr_probe(struct auxiliary_device *auxdev, const struct auxiliary_device_id *id)
 {
 	struct oobmsm_plat_info *plat_info;
@@ -282,10 +309,16 @@ static int intel_plr_probe(struct auxiliary_device *auxdev, const struct auxilia
 	if (!plr)
 		return -ENOMEM;
 
+	mutex_init(&plr->lock);
+
+	intel_plr_register_notifier(&plr->nb);
+
 	plr->die_info = devm_kcalloc(&auxdev->dev, num_resources, sizeof(*plr->die_info),
 				     GFP_KERNEL);
-	if (!plr->die_info)
-		return -ENOMEM;
+	if (!plr->die_info) {
+		err = -ENOMEM;
+		goto err_notify;
+	}
 
 	plr->num_dies = num_resources;
 	plr->dbgfs_dir = debugfs_create_dir("plr", dentry);
@@ -326,6 +359,9 @@ static int intel_plr_probe(struct auxiliary_device *auxdev, const struct auxilia
 
 err:
 	debugfs_remove_recursive(plr->dbgfs_dir);
+err_notify:
+	intel_plr_unregister_notifier(&plr->nb);
+
 	return err;
 }
 
@@ -333,6 +369,9 @@ static void intel_plr_remove(struct auxiliary_device *auxdev)
 {
 	struct tpmi_plr *plr = auxiliary_get_drvdata(auxdev);
 
+	intel_plr_unregister_notifier(&plr->nb);
+
+	guard(mutex)(&plr->lock);
 	debugfs_remove_recursive(plr->dbgfs_dir);
 }
 
-- 
2.52.0