x86/cpu: Provide debug interface

Provide debug files which dump the topology related information of
cpuinfo_x86. This is useful to validate the upcoming conversion of the
topology evaluation for correctness or bug compatibility.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Juergen Gross <jgross@suse.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230814085113.353191313@linutronix.de

Author: KAGA-KOKO

arch/x86/kernel/cpu/Makefile

@@ -54,6 +54,8 @@ obj-$(CONFIG_X86_LOCAL_APIC)		+= perfctr-watchdog.o
 obj-$(CONFIG_HYPERVISOR_GUEST)		+= vmware.o hypervisor.o mshyperv.o
 obj-$(CONFIG_ACRN_GUEST)		+= acrn.o
 
+obj-$(CONFIG_DEBUG_FS)			+= debugfs.o
+
 quiet_cmd_mkcapflags = MKCAP   $@
       cmd_mkcapflags = $(CONFIG_SHELL) $(srctree)/$(src)/mkcapflags.sh $@ $^
 

arch/x86/kernel/cpu/debugfs.c

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/debugfs.h>
+
+#include <asm/apic.h>
+#include <asm/processor.h>
+
+static int cpu_debug_show(struct seq_file *m, void *p)
+{
+	unsigned long cpu = (unsigned long)m->private;
+	struct cpuinfo_x86 *c = per_cpu_ptr(&cpu_info, cpu);
+
+	seq_printf(m, "online:              %d\n", cpu_online(cpu));
+	if (!c->initialized)
+		return 0;
+
+	seq_printf(m, "initial_apicid:      %x\n", c->topo.initial_apicid);
+	seq_printf(m, "apicid:              %x\n", c->topo.apicid);
+	seq_printf(m, "pkg_id:              %u\n", c->topo.pkg_id);
+	seq_printf(m, "die_id:              %u\n", c->topo.die_id);
+	seq_printf(m, "cu_id:               %u\n", c->topo.cu_id);
+	seq_printf(m, "core_id:             %u\n", c->topo.core_id);
+	seq_printf(m, "logical_pkg_id:      %u\n", c->topo.logical_pkg_id);
+	seq_printf(m, "logical_die_id:      %u\n", c->topo.logical_die_id);
+	seq_printf(m, "llc_id:              %u\n", c->topo.llc_id);
+	seq_printf(m, "l2c_id:              %u\n", c->topo.l2c_id);
+	seq_printf(m, "max_cores:           %u\n", c->x86_max_cores);
+	seq_printf(m, "max_die_per_pkg:     %u\n", __max_die_per_package);
+	seq_printf(m, "smp_num_siblings:    %u\n", smp_num_siblings);
+	return 0;
+}
+
+static int cpu_debug_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, cpu_debug_show, inode->i_private);
+}
+
+static const struct file_operations dfs_cpu_ops = {
+	.open		= cpu_debug_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static __init int cpu_init_debugfs(void)
+{
+	struct dentry *dir, *base = debugfs_create_dir("topo", arch_debugfs_dir);
+	unsigned long id;
+	char name[24];
+
+	dir = debugfs_create_dir("cpus", base);
+	for_each_possible_cpu(id) {
+		sprintf(name, "%lu", id);
+		debugfs_create_file(name, 0444, dir, (void *)id, &dfs_cpu_ops);
+	}
+	return 0;
+}
+late_initcall(cpu_init_debugfs);