powerpc/pseries/dlpar: Remove device tree node for DLPAR IO remove

In the powerpc-pseries specific implementation, the IO hotplug
event is handled in the user space (drmgr tool). But update the
device tree and /dev/mem access to allocate buffers for some
RTAS calls are restricted when the kernel lockdown feature is
enabled. For the DLPAR IO REMOVE, the corresponding device tree
nodes and properties have to be removed from the device tree
after the device disable. The user space removes the device tree
nodes by updating /proc/ppc64/ofdt which is not allowed  under
system lockdown is enabled. This restriction can be resolved
by moving the complete IO hotplug handling in the kernel. But
the pseries implementation need user interaction to power off
and to remove device from the slot during hotplug event handling.

To overcome the /proc/ppc64/ofdt restriction, this patch extends
the /sys/kernel/dlpar interface and provides
‘dt remove index <drc_index>’ to the user space so that drmgr
tool can remove the corresponding device tree nodes based on DRC
index from the device tree.

Signed-off-by: Scott Cheloha <cheloha@linux.ibm.com>
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240822025028.938332-2-haren@linux.ibm.com

Author: hmyneni

arch/powerpc/include/asm/rtas.h

@@ -397,6 +397,7 @@ inline uint16_t pseries_errorlog_length(struct pseries_errorlog *sect)
 #define PSERIES_HP_ELOG_RESOURCE_SLOT	3
 #define PSERIES_HP_ELOG_RESOURCE_PHB	4
 #define PSERIES_HP_ELOG_RESOURCE_PMEM   6
+#define PSERIES_HP_ELOG_RESOURCE_DT	7
 
 #define PSERIES_HP_ELOG_ACTION_ADD	1
 #define PSERIES_HP_ELOG_ACTION_REMOVE	2

arch/powerpc/platforms/pseries/dlpar.c

@@ -327,6 +327,87 @@ int dlpar_unisolate_drc(u32 drc_index)
 	return 0;
 }
 
+static int changeset_detach_node_recursive(struct of_changeset *ocs,
+					struct device_node *node)
+{
+	struct device_node *child;
+	int rc;
+
+	for_each_child_of_node(node, child) {
+		rc = changeset_detach_node_recursive(ocs, child);
+		if (rc) {
+			of_node_put(child);
+			return rc;
+		}
+	}
+
+	return of_changeset_detach_node(ocs, node);
+}
+
+static int dlpar_hp_dt_remove(u32 drc_index)
+{
+	struct device_node *np;
+	struct of_changeset ocs;
+	u32 index;
+	int rc = 0;
+
+	/*
+	 * Prune all nodes with a matching index.
+	 */
+	of_changeset_init(&ocs);
+
+	for_each_node_with_property(np, "ibm,my-drc-index") {
+		rc = of_property_read_u32(np, "ibm,my-drc-index", &index);
+		if (rc) {
+			pr_err("%s: %pOF: of_property_read_u32 %s: %d\n",
+				__func__, np, "ibm,my-drc-index", rc);
+			of_node_put(np);
+			goto out;
+		}
+
+		if (index == drc_index) {
+			rc = changeset_detach_node_recursive(&ocs, np);
+			if (rc) {
+				of_node_put(np);
+				goto out;
+			}
+		}
+	}
+
+	rc = of_changeset_apply(&ocs);
+
+out:
+	of_changeset_destroy(&ocs);
+	return rc;
+}
+
+static int dlpar_hp_dt(struct pseries_hp_errorlog *phpe)
+{
+	u32 drc_index;
+	int rc;
+
+	if (phpe->id_type != PSERIES_HP_ELOG_ID_DRC_INDEX)
+		return -EINVAL;
+
+	drc_index = be32_to_cpu(phpe->_drc_u.drc_index);
+
+	lock_device_hotplug();
+
+	switch (phpe->action) {
+	case PSERIES_HP_ELOG_ACTION_REMOVE:
+		rc = dlpar_hp_dt_remove(drc_index);
+		break;
+	default:
+		pr_err("Invalid action (%d) specified\n", phpe->action);
+		rc = -EINVAL;
+		break;
+	}
+
+	unlock_device_hotplug();
+
+	return rc;
+}
+
 int handle_dlpar_errorlog(struct pseries_hp_errorlog *hp_elog)
 {
 	int rc;
@@ -341,6 +422,9 @@ int handle_dlpar_errorlog(struct pseries_hp_errorlog *hp_elog)
 	case PSERIES_HP_ELOG_RESOURCE_PMEM:
 		rc = dlpar_hp_pmem(hp_elog);
 		break;
+	case PSERIES_HP_ELOG_RESOURCE_DT:
+		rc = dlpar_hp_dt(hp_elog);
+		break;
 
 	default:
 		pr_warn_ratelimited("Invalid resource (%d) specified\n",
@@ -393,6 +477,8 @@ static int dlpar_parse_resource(char **cmd, struct pseries_hp_errorlog *hp_elog)
 		hp_elog->resource = PSERIES_HP_ELOG_RESOURCE_MEM;
 	} else if (sysfs_streq(arg, "cpu")) {
 		hp_elog->resource = PSERIES_HP_ELOG_RESOURCE_CPU;
+	} else if (sysfs_streq(arg, "dt")) {
+		hp_elog->resource = PSERIES_HP_ELOG_RESOURCE_DT;
 	} else {
 		pr_err("Invalid resource specified.\n");
 		return -EINVAL;
@@ -534,7 +620,7 @@ static ssize_t dlpar_store(const struct class *class, const struct class_attribu
 static ssize_t dlpar_show(const struct class *class, const struct class_attribute *attr,
 			  char *buf)
 {
-	return sprintf(buf, "%s\n", "memory,cpu");
+	return sprintf(buf, "%s\n", "memory,cpu,dt");
 }
 
 static CLASS_ATTR_RW(dlpar);