x86/cpu: Provide cpu_init/parse_topology()

Topology evaluation is a complete disaster and impenetrable mess. It's
scattered all over the place with some vendor implementations doing early
evaluation and some not. The most horrific part is the permanent
overwriting of smt_max_siblings and __max_die_per_package, instead of
establishing them once on the boot CPU and validating the result on the
APs.

The goals are:

  - One topology evaluation entry point

  - Proper sharing of pointlessly duplicated code

  - Proper structuring of the evaluation logic and preferences.

  - Evaluating important system wide information only once on the boot CPU

  - Making the 0xb/0x1f leaf parsing less convoluted and actually fixing
    the short comings of leaf 0x1f evaluation.

Start to consolidate the topology evaluation code by providing the entry
points for the early boot CPU evaluation and for the final parsing on the
boot CPU and the APs.

Move the trivial pieces into that new code:

   - The initialization of cpuinfo_x86::topo

   - The evaluation of CPUID leaf 1, which presets topo::initial_apicid

   - topo_apicid is set to topo::initial_apicid when invoked from early
     boot. When invoked for the final evaluation on the boot CPU it reads
     the actual APIC ID, which makes apic_get_initial_apicid() obsolete
     once everything is converted over.

Provide a temporary helper function topo_converted() which shields off the
not yet converted CPU vendors from invoking code which would break them.
This shielding covers all vendor CPUs which support SMP, but not the
historical pure UP ones as they only need the topology info init and
eventually the initial APIC initialization.

Provide two new members in cpuinfo_x86::topo to store the maximum number of
SMT siblings and the number of dies per package and add them to the debugfs
readout. These two members will be used to populate this information on the
boot CPU and to validate the APs against it.
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 <mhklinux@outlook.com>
Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Zhang Rui <rui.zhang@intel.com>
Tested-by: Wang Wendy <wendy.wang@intel.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240212153624.581436579@linutronix.de

arch/x86/include/asm/topology.h

@@ -102,6 +102,25 @@ static inline void setup_node_to_cpumask_map(void) { }
 
 #include <asm-generic/topology.h>
 
+/* Topology information */
+enum x86_topology_domains {
+	TOPO_SMT_DOMAIN,
+	TOPO_CORE_DOMAIN,
+	TOPO_MODULE_DOMAIN,
+	TOPO_TILE_DOMAIN,
+	TOPO_DIE_DOMAIN,
+	TOPO_DIEGRP_DOMAIN,
+	TOPO_PKG_DOMAIN,
+	TOPO_MAX_DOMAIN,
+};
+
+struct x86_topology_system {
+	unsigned int	dom_shifts[TOPO_MAX_DOMAIN];
+	unsigned int	dom_size[TOPO_MAX_DOMAIN];
+};
+
+extern struct x86_topology_system x86_topo_system;
+
 extern const struct cpumask *cpu_coregroup_mask(int cpu);
 extern const struct cpumask *cpu_clustergroup_mask(int cpu);
 

arch/x86/kernel/cpu/Makefile

@@ -17,7 +17,8 @@ KMSAN_SANITIZE_common.o := n
 # As above, instrumenting secondary CPU boot code causes boot hangs.
 KCSAN_SANITIZE_common.o := n
 
-obj-y			:= cacheinfo.o scattered.o topology.o
+obj-y			:= cacheinfo.o scattered.o
+obj-y			+= topology_common.o topology.o
 obj-y			+= common.o
 obj-y			+= rdrand.o
 obj-y			+= match.o

arch/x86/kernel/cpu/common.c

@@ -1591,6 +1591,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 		setup_force_cpu_cap(X86_FEATURE_CPUID);
 		cpu_parse_early_param();
 
+		cpu_init_topology(c);
+
 		if (this_cpu->c_early_init)
 			this_cpu->c_early_init(c);
 
@@ -1601,6 +1603,7 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 			this_cpu->c_bsp_init(c);
 	} else {
 		setup_clear_cpu_cap(X86_FEATURE_CPUID);
+		cpu_init_topology(c);
 	}
 
 	get_cpu_address_sizes(c);
@@ -1748,18 +1751,6 @@ static void generic_identify(struct cpuinfo_x86 *c)
 
 	get_cpu_address_sizes(c);
 
-	if (c->cpuid_level >= 0x00000001) {
-		c->topo.initial_apicid = (cpuid_ebx(1) >> 24) & 0xFF;
-#ifdef CONFIG_X86_32
-# ifdef CONFIG_SMP
-		c->topo.apicid = apic->phys_pkg_id(c->topo.initial_apicid, 0);
-# else
-		c->topo.apicid = c->topo.initial_apicid;
-# endif
-#endif
-		c->topo.pkg_id = c->topo.initial_apicid;
-	}
-
 	get_model_name(c); /* Default name */
 
 	/*
@@ -1818,9 +1809,6 @@ static void identify_cpu(struct cpuinfo_x86 *c)
 	c->x86_model_id[0] = '\0';  /* Unset */
 	c->x86_max_cores = 1;
 	c->x86_coreid_bits = 0;
-	c->topo.cu_id = 0xff;
-	c->topo.llc_id = BAD_APICID;
-	c->topo.l2c_id = BAD_APICID;
 #ifdef CONFIG_X86_64
 	c->x86_clflush_size = 64;
 	c->x86_phys_bits = 36;
@@ -1839,6 +1827,8 @@ static void identify_cpu(struct cpuinfo_x86 *c)
 
 	generic_identify(c);
 
+	cpu_parse_topology(c);
+
 	if (this_cpu->c_identify)
 		this_cpu->c_identify(c);
 
@@ -1846,10 +1836,10 @@ static void identify_cpu(struct cpuinfo_x86 *c)
 	apply_forced_caps(c);
 
 #ifdef CONFIG_X86_64
-	c->topo.apicid = apic->phys_pkg_id(c->topo.initial_apicid, 0);
+	if (!topo_is_converted(c))
+		c->topo.apicid = apic->phys_pkg_id(c->topo.initial_apicid, 0);
 #endif
 
-
 	/*
 	 * Set default APIC and TSC_DEADLINE MSR fencing flag. AMD and
 	 * Hygon will clear it in ->c_init() below.

arch/x86/kernel/cpu/cpu.h

@@ -2,6 +2,11 @@
 #ifndef ARCH_X86_CPU_H
 #define ARCH_X86_CPU_H
 
+#include <asm/cpu.h>
+#include <asm/topology.h>
+
+#include "topology.h"
+
 /* attempt to consolidate cpu attributes */
 struct cpu_dev {
 	const char	*c_vendor;
@@ -96,4 +101,5 @@ static inline bool spectre_v2_in_eibrs_mode(enum spectre_v2_mitigation mode)
 	       mode == SPECTRE_V2_EIBRS_RETPOLINE ||
 	       mode == SPECTRE_V2_EIBRS_LFENCE;
 }
+
 #endif /* ARCH_X86_CPU_H */

arch/x86/kernel/cpu/debugfs.c

@@ -5,6 +5,8 @@
 #include <asm/apic.h>
 #include <asm/processor.h>
 
+#include "cpu.h"
+
 static int cpu_debug_show(struct seq_file *m, void *p)
 {
 	unsigned long cpu = (unsigned long)m->private;
@@ -42,12 +44,48 @@ static const struct file_operations dfs_cpu_ops = {
 	.release	= single_release,
 };
 
+static int dom_debug_show(struct seq_file *m, void *p)
+{
+	static const char *domain_names[TOPO_MAX_DOMAIN] = {
+		[TOPO_SMT_DOMAIN]	= "Thread",
+		[TOPO_CORE_DOMAIN]	= "Core",
+		[TOPO_MODULE_DOMAIN]	= "Module",
+		[TOPO_TILE_DOMAIN]	= "Tile",
+		[TOPO_DIE_DOMAIN]	= "Die",
+		[TOPO_DIEGRP_DOMAIN]	= "DieGrp",
+		[TOPO_PKG_DOMAIN]	= "Package",
+	};
+	unsigned int dom, nthreads = 1;
+
+	for (dom = 0; dom < TOPO_MAX_DOMAIN; dom++) {
+		nthreads *= x86_topo_system.dom_size[dom];
+		seq_printf(m, "domain: %-10s shift: %u dom_size: %5u max_threads: %5u\n",
+			   domain_names[dom], x86_topo_system.dom_shifts[dom],
+			   x86_topo_system.dom_size[dom], nthreads);
+	}
+	return 0;
+}
+
+static int dom_debug_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, dom_debug_show, inode->i_private);
+}
+
+static const struct file_operations dfs_dom_ops = {
+	.open		= dom_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];
 
+	debugfs_create_file("domains", 0444, base, NULL, &dfs_dom_ops);
+
 	dir = debugfs_create_dir("cpus", base);
 	for_each_possible_cpu(id) {
 		sprintf(name, "%lu", id);

arch/x86/kernel/cpu/topology.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef ARCH_X86_TOPOLOGY_H
+#define ARCH_X86_TOPOLOGY_H
+
+struct topo_scan {
+	struct cpuinfo_x86	*c;
+	unsigned int		dom_shifts[TOPO_MAX_DOMAIN];
+	unsigned int		dom_ncpus[TOPO_MAX_DOMAIN];
+};
+
+bool topo_is_converted(struct cpuinfo_x86 *c);
+void cpu_init_topology(struct cpuinfo_x86 *c);
+void cpu_parse_topology(struct cpuinfo_x86 *c);
+void topology_set_dom(struct topo_scan *tscan, enum x86_topology_domains dom,
+		      unsigned int shift, unsigned int ncpus);
+
+static inline u32 topo_shift_apicid(u32 apicid, enum x86_topology_domains dom)
+{
+	if (dom == TOPO_SMT_DOMAIN)
+		return apicid;
+	return apicid >> x86_topo_system.dom_shifts[dom - 1];
+}
+
+static inline u32 topo_relative_domain_id(u32 apicid, enum x86_topology_domains dom)
+{
+	if (dom != TOPO_SMT_DOMAIN)
+		apicid >>= x86_topo_system.dom_shifts[dom - 1];
+	return apicid & (x86_topo_system.dom_size[dom] - 1);
+}
+
+static inline u32 topo_domain_mask(enum x86_topology_domains dom)
+{
+	return (1U << x86_topo_system.dom_shifts[dom]) - 1;
+}
+
+#endif /* ARCH_X86_TOPOLOGY_H */

arch/x86/kernel/cpu/topology_common.c

+// SPDX-License-Identifier: GPL-2.0
+#include <linux/cpu.h>
+
+#include <xen/xen.h>
+
+#include <asm/apic.h>
+#include <asm/processor.h>
+#include <asm/smp.h>
+
+#include "cpu.h"
+
+struct x86_topology_system x86_topo_system __ro_after_init;
+
+void topology_set_dom(struct topo_scan *tscan, enum x86_topology_domains dom,
+		      unsigned int shift, unsigned int ncpus)
+{
+	tscan->dom_shifts[dom] = shift;
+	tscan->dom_ncpus[dom] = ncpus;
+
+	/* Propagate to the upper levels */
+	for (dom++; dom < TOPO_MAX_DOMAIN; dom++) {
+		tscan->dom_shifts[dom] = tscan->dom_shifts[dom - 1];
+		tscan->dom_ncpus[dom] = tscan->dom_ncpus[dom - 1];
+	}
+}
+
+bool topo_is_converted(struct cpuinfo_x86 *c)
+{
+	/* Temporary until everything is converted over. */
+	switch (boot_cpu_data.x86_vendor) {
+	case X86_VENDOR_AMD:
+	case X86_VENDOR_CENTAUR:
+	case X86_VENDOR_INTEL:
+	case X86_VENDOR_HYGON:
+	case X86_VENDOR_ZHAOXIN:
+		return false;
+	default:
+		/* Let all UP systems use the below */
+		return true;
+	}
+}
+
+static bool fake_topology(struct topo_scan *tscan)
+{
+	/*
+	 * Preset the CORE level shift for CPUID less systems and XEN_PV,
+	 * which has useless CPUID information.
+	 */
+	topology_set_dom(tscan, TOPO_SMT_DOMAIN, 0, 1);
+	topology_set_dom(tscan, TOPO_CORE_DOMAIN, 1, 1);
+
+	return tscan->c->cpuid_level < 1 || xen_pv_domain();
+}
+
+static void parse_topology(struct topo_scan *tscan, bool early)
+{
+	const struct cpuinfo_topology topo_defaults = {
+		.cu_id			= 0xff,
+		.llc_id			= BAD_APICID,
+		.l2c_id			= BAD_APICID,
+	};
+	struct cpuinfo_x86 *c = tscan->c;
+	struct {
+		u32	unused0		: 16,
+			nproc		:  8,
+			apicid		:  8;
+	} ebx;
+
+	c->topo = topo_defaults;
+
+	if (fake_topology(tscan))
+		return;
+
+	/* Preset Initial APIC ID from CPUID leaf 1 */
+	cpuid_leaf_reg(1, CPUID_EBX, &ebx);
+	c->topo.initial_apicid = ebx.apicid;
+
+	/*
+	 * The initial invocation from early_identify_cpu() happens before
+	 * the APIC is mapped or X2APIC enabled. For establishing the
+	 * topology, that's not required. Use the initial APIC ID.
+	 */
+	if (early)
+		c->topo.apicid = c->topo.initial_apicid;
+	else
+		c->topo.apicid = read_apic_id();
+
+	/* The above is sufficient for UP */
+	if (!IS_ENABLED(CONFIG_SMP))
+		return;
+}
+
+static void topo_set_ids(struct topo_scan *tscan)
+{
+	struct cpuinfo_x86 *c = tscan->c;
+	u32 apicid = c->topo.apicid;
+
+	c->topo.pkg_id = topo_shift_apicid(apicid, TOPO_PKG_DOMAIN);
+	c->topo.die_id = topo_shift_apicid(apicid, TOPO_DIE_DOMAIN);
+
+	/* Package relative core ID */
+	c->topo.core_id = (apicid & topo_domain_mask(TOPO_PKG_DOMAIN)) >>
+		x86_topo_system.dom_shifts[TOPO_SMT_DOMAIN];
+}
+
+static void topo_set_max_cores(struct topo_scan *tscan)
+{
+	/*
+	 * Bug compatible for now. This is broken on hybrid systems:
+	 * 8 cores SMT + 8 cores w/o SMT
+	 * tscan.dom_ncpus[TOPO_DIEGRP_DOMAIN] = 24; 24 / 2 = 12 !!
+	 *
+	 * Cannot be fixed without further topology enumeration changes.
+	 */
+	tscan->c->x86_max_cores = tscan->dom_ncpus[TOPO_DIEGRP_DOMAIN] >>
+		x86_topo_system.dom_shifts[TOPO_SMT_DOMAIN];
+}
+
+void cpu_parse_topology(struct cpuinfo_x86 *c)
+{
+	unsigned int dom, cpu = smp_processor_id();
+	struct topo_scan tscan = { .c = c, };
+
+	parse_topology(&tscan, false);
+
+	if (!topo_is_converted(c))
+		return;
+
+	for (dom = TOPO_SMT_DOMAIN; dom < TOPO_MAX_DOMAIN; dom++) {
+		if (tscan.dom_shifts[dom] == x86_topo_system.dom_shifts[dom])
+			continue;
+		pr_err(FW_BUG "CPU%d: Topology domain %u shift %u != %u\n", cpu, dom,
+		       tscan.dom_shifts[dom], x86_topo_system.dom_shifts[dom]);
+	}
+
+	/* Bug compatible with the existing parsers */
+	if (tscan.dom_ncpus[TOPO_SMT_DOMAIN] > smp_num_siblings) {
+		if (system_state == SYSTEM_BOOTING) {
+			pr_warn_once("CPU%d: SMT detected and enabled late\n", cpu);
+			smp_num_siblings = tscan.dom_ncpus[TOPO_SMT_DOMAIN];
+		} else {
+			pr_warn_once("CPU%d: SMT detected after init. Too late!\n", cpu);
+		}
+	}
+
+	topo_set_ids(&tscan);
+	topo_set_max_cores(&tscan);
+}
+
+void __init cpu_init_topology(struct cpuinfo_x86 *c)
+{
+	struct topo_scan tscan = { .c = c, };
+	unsigned int dom, sft;
+
+	parse_topology(&tscan, true);
+
+	if (!topo_is_converted(c))
+		return;
+
+	/* Copy the shift values and calculate the unit sizes. */
+	memcpy(x86_topo_system.dom_shifts, tscan.dom_shifts, sizeof(x86_topo_system.dom_shifts));
+
+	dom = TOPO_SMT_DOMAIN;
+	x86_topo_system.dom_size[dom] = 1U << x86_topo_system.dom_shifts[dom];
+
+	for (dom++; dom < TOPO_MAX_DOMAIN; dom++) {
+		sft = x86_topo_system.dom_shifts[dom] - x86_topo_system.dom_shifts[dom - 1];
+		x86_topo_system.dom_size[dom] = 1U << sft;
+	}
+
+	topo_set_ids(&tscan);
+	topo_set_max_cores(&tscan);
+
+	/*
+	 * Bug compatible with the existing code. If the boot CPU does not
+	 * have SMT this ends up with one sibling. This needs way deeper
+	 * changes further down the road to get it right during early boot.
+	 */
+	smp_num_siblings = tscan.dom_ncpus[TOPO_SMT_DOMAIN];
+
+	/*
+	 * Neither it's clear whether there are as many dies as the APIC
+	 * space indicating die level is. But assume that the actual number
+	 * of CPUs gives a proper indication for now to stay bug compatible.
+	 */
+	__max_die_per_package = tscan.dom_ncpus[TOPO_DIE_DOMAIN] /
+		tscan.dom_ncpus[TOPO_DIE_DOMAIN - 1];
+}