[RFC PATCH 18/46] liveupdate: cpu_preserve: Add LUO file handler for preserved physical CPUs

[Pasha Tatashin]

Implement the LUO file handler (cpu_preserve_handler) and early boot
incoming CPU adoption for /sys/devices/system/cpu/cpuX/preserve fds.

Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
---
 kernel/liveupdate/cpu_preserve.c | 189 ++++++++++++++++++++++++++++++-
 1 file changed, 185 insertions(+), 4 deletions(-)

diff --git a/kernel/liveupdate/cpu_preserve.c b/kernel/liveupdate/cpu_preserve.c
index 2f92dfee82b1..9a039ba9e912 100644
--- a/kernel/liveupdate/cpu_preserve.c
+++ b/kernel/liveupdate/cpu_preserve.c
@@ -837,8 +837,10 @@ void __cpu_preserved_text cpu_preserved_set_dead(int cpu)
 {
 	struct cpu_preserved_pcpu_ser *ser = cpu_preserved_get_pcpu_ser(cpu);
 
-	if (ser)
-		WRITE_ONCE(ser->workload, CPU_PRESERVED_DEAD);
+	if (ser) {
+		smp_store_release(&ser->workload, CPU_PRESERVED_DEAD);
+		cpu_preserved_clean(ser);
+	}
 }
 EXPORT_SYMBOL_GPL(cpu_preserved_set_dead);
 
@@ -1097,8 +1099,6 @@ void __cpu_preserved_text cpu_preserved_park_loop(int cpu)
 		switch (READ_ONCE(ser->workload)) {
 		case CPU_PRESERVED_EXITING:
 		case CPU_PRESERVED_DEAD:
-			WRITE_ONCE(ser->workload, CPU_PRESERVED_DEAD);
-			cpu_preserved_clean(ser);
 			return;
 		case CPU_PRESERVED_WORKLOAD:
 			cpu_preserved_run_workload(ser, pcpu);
@@ -1131,6 +1131,7 @@ void cpu_preserved_park(int cpu)
 	} else {
 		cpu_preserved_park_loop(cpu);
 		arch_cpu_preserved_park_finish(cpu);
+		cpu_preserved_set_dead(cpu);
 	}
 }
 EXPORT_SYMBOL_GPL(cpu_preserved_park);
@@ -1498,6 +1499,171 @@ static struct liveupdate_flb cpu_preserved_flb = {
 	.compatible = CPU_PRESERVED_LUO_FLB_COMPATIBLE,
 };
 
+/*
+ * LUO File Handler Callbacks for /sys/devices/system/cpu/cpu<N>/preserve
+ */
+static int file_to_cpu(struct file *file, unsigned int *cpup)
+{
+	struct dentry *dentry, *parent;
+	unsigned int cpu;
+
+	if (!file || !file->f_path.dentry)
+		return -EINVAL;
+
+	if (file_inode(file)->i_sb->s_magic != SYSFS_MAGIC)
+		return -EINVAL;
+
+	dentry = file->f_path.dentry;
+	if (strcmp(dentry->d_name.name, "preserve"))
+		return -EINVAL;
+
+	parent = dentry->d_parent;
+	if (!parent || sscanf(parent->d_name.name, "cpu%u", &cpu) != 1)
+		return -EINVAL;
+
+	if (cpu >= nr_cpu_ids || !cpu_possible(cpu) ||
+	    !cpu_is_hotpluggable(cpu)) {
+		return -EINVAL;
+	}
+
+	*cpup = cpu;
+	return 0;
+}
+
+static bool cpu_preserve_can_preserve(struct liveupdate_file_handler *handler,
+				      struct file *file)
+{
+	unsigned int cpu;
+
+	return IS_ENABLED(CONFIG_LIVEUPDATE_ONCORE) && file_to_cpu(file, &cpu) == 0;
+}
+
+static int cpu_preserve_preserve(struct liveupdate_file_op_args *args)
+{
+	struct cpu_preserved_file_ser *fser;
+	unsigned int cpu;
+	int ret;
+
+	ret = file_to_cpu(args->file, &cpu);
+	if (ret)
+		return ret;
+
+	ret = cpu_preserve(cpu);
+	if (ret)
+		return ret;
+
+	fser = kho_alloc_preserve(sizeof(*fser));
+	if (IS_ERR(fser)) {
+		cpu_unpreserve(cpu);
+		return PTR_ERR(fser);
+	}
+
+	memset(fser, 0, sizeof(*fser));
+	fser->cpu = cpu;
+
+	scoped_guard(mutex, &cpu_preserved_lock)
+		fser->stack_pa = cpu_preserved_outgoing.pcpus[cpu].stack_pa;
+
+	args->serialized_data = virt_to_phys(fser);
+	return 0;
+}
+
+static void cpu_preserve_unpreserve(struct liveupdate_file_op_args *args)
+{
+	struct cpu_preserved_file_ser *fser;
+	unsigned int cpu;
+
+	if (!args->serialized_data)
+		return;
+
+	fser = phys_to_virt(args->serialized_data);
+	cpu = fser->cpu;
+
+	cpu_unpreserve(cpu);
+
+	kho_unpreserve_free(fser);
+}
+
+static void cpu_preserve_restore_incoming_cpu(struct liveupdate_session *session,
+					      struct cpu_preserved_file_ser *fser)
+{
+	unsigned int cpu = fser->cpu;
+
+	scoped_guard(mutex, &cpu_preserved_lock) {
+		cpumask_set_cpu(cpu, &cpu_preserved_incoming.mask);
+		cpumask_set_cpu(cpu, &cpu_preserved_mask);
+
+		if (!cpu_preserved_incoming.pcpus) {
+			cpu_preserved_incoming.pcpus =
+				kcalloc(nr_cpu_ids,
+					sizeof(*cpu_preserved_incoming.pcpus),
+					GFP_KERNEL);
+			WRITE_ONCE(cpu_preserved_host_pcpus_va,
+				   cpu_preserved_incoming.pcpus);
+			cpu_preserved_clean(&cpu_preserved_host_pcpus_va);
+		}
+
+		if (cpu_preserved_incoming.pcpus)
+			cpu_preserved_incoming.pcpus[cpu].stack_pa = fser->stack_pa;
+
+		cpu_preserved_clean(&cpu_preserved_mask);
+	}
+}
+
+static int cpu_preserve_retrieve(struct liveupdate_file_op_args *args)
+{
+	struct cpu_preserved_file_ser *fser;
+	struct file *file;
+	char path[64];
+
+	if (!args->serialized_data)
+		return -EINVAL;
+
+	fser = phys_to_virt(args->serialized_data);
+
+	snprintf(path, sizeof(path),
+		 "/sys/devices/system/cpu/cpu%u/preserve", fser->cpu);
+	file = filp_open(path, O_RDONLY, 0);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	args->file = file;
+	cpu_preserve_restore_incoming_cpu(args->session, fser);
+	cpu_preserved_detach_workload(fser->cpu);
+
+	return 0;
+}
+
+static void cpu_preserve_finish(struct liveupdate_file_op_args *args)
+{
+	struct cpu_preserved_file_ser *fser;
+
+	if (!args->serialized_data)
+		return;
+
+	fser = phys_to_virt(args->serialized_data);
+	if (args->retrieve_status <= 0)
+		cpu_preserve_restore_incoming_cpu(args->session, fser);
+
+	cpu_unpreserve(fser->cpu);
+
+	kho_restore_free(fser);
+}
+
+static const struct liveupdate_file_ops cpu_preserve_file_ops = {
+	.can_preserve = cpu_preserve_can_preserve,
+	.preserve     = cpu_preserve_preserve,
+	.retrieve     = cpu_preserve_retrieve,
+	.unpreserve   = cpu_preserve_unpreserve,
+	.finish       = cpu_preserve_finish,
+	.owner        = THIS_MODULE,
+};
+
+static struct liveupdate_file_handler cpu_preserve_handler = {
+	.ops        = &cpu_preserve_file_ops,
+	.compatible = CPU_PRESERVED_LUO_FH_COMPATIBLE,
+};
+
 static int cpu_preserve_reboot_notify(struct notifier_block *nb,
 				      unsigned long action, void *data)
 {
@@ -1555,6 +1721,21 @@ static int __init cpu_preserve_early_init(void)
 	cpu_preserved_incoming.pcpus_ser = NULL;
 	cpu_preserved_global_ser = NULL;
 
+	err = liveupdate_register_file_handler(&cpu_preserve_handler);
+	if (err && err != -EOPNOTSUPP) {
+		pr_err("Could not register cpu_preserve file handler: %pe\n",
+		       ERR_PTR(err));
+		return err;
+	}
+
+	err = liveupdate_register_flb(&cpu_preserve_handler,
+				      &cpu_preserved_flb);
+	if (err && err != -EOPNOTSUPP) {
+		pr_err("Could not register cpu_preserved FLB: %pe\n",
+		       ERR_PTR(err));
+		return err;
+	}
+
 	/* Retrieve incoming preserved CPUs before secondary CPU bringup */
 	if (liveupdate_enabled())
 		liveupdate_flb_get_incoming(&cpu_preserved_flb, &obj);
-- 
2.55.0.1082.g2b9226bbc0-goog