x86/cpu: Provide a sane leaf 0xb/0x1f parser

detect_extended_topology() along with it's early() variant is a classic
example for duct tape engineering:

  - It evaluates an array of subleafs with a boatload of local variables
    for the relevant topology levels instead of using an array to save the
    enumerated information and propagate it to the right level

  - It has no boundary checks for subleafs

  - It prevents updating the die_id with a crude workaround instead of
    checking for leaf 0xb which does not provide die information.

  - It's broken vs. the number of dies evaluation as it uses:

      num_processors[DIE_LEVEL] / num_processors[CORE_LEVEL]

    which "works" only correctly if there is none of the intermediate
    topology levels (MODULE/TILE) enumerated.

There is zero value in trying to "fix" that code as the only proper fix is
to rewrite it from scratch.

Implement a sane parser with proper code documentation, which will be used
for the consolidated topology evaluation in the next step.
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: Zhang Rui <rui.zhang@intel.com>
Tested-by: Wang Wendy <wendy.wang@intel.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20240212153624.830571770@linutronix.de

arch/x86/kernel/cpu/Makefile

@@ -18,7 +18,7 @@ KMSAN_SANITIZE_common.o := n
 KCSAN_SANITIZE_common.o := n
 
 obj-y			:= cacheinfo.o scattered.o
-obj-y			+= topology_common.o topology.o
+obj-y			+= topology_common.o topology_ext.o topology.o
 obj-y			+= common.o
 obj-y			+= rdrand.o
 obj-y			+= match.o

arch/x86/kernel/cpu/topology.h

@@ -16,6 +16,7 @@ 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);
+bool cpu_parse_topology_ext(struct topo_scan *tscan);
 
 static inline u32 topo_shift_apicid(u32 apicid, enum x86_topology_domains dom)
 {
@@ -36,4 +37,15 @@ static inline u32 topo_domain_mask(enum x86_topology_domains dom)
 	return (1U << x86_topo_system.dom_shifts[dom]) - 1;
 }
 
+/*
+ * Update a domain level after the fact without propagating. Used to fixup
+ * broken CPUID enumerations.
+ */
+static inline void topology_update_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;
+}
+
 #endif /* ARCH_X86_TOPOLOGY_H */

arch/x86/kernel/cpu/topology_ext.c

+// SPDX-License-Identifier: GPL-2.0
+#include <linux/cpu.h>
+
+#include <asm/apic.h>
+#include <asm/memtype.h>
+#include <asm/processor.h>
+
+#include "cpu.h"
+
+enum topo_types {
+	INVALID_TYPE		= 0,
+	SMT_TYPE		= 1,
+	CORE_TYPE		= 2,
+	MAX_TYPE_0B		= 3,
+	MODULE_TYPE		= 3,
+	TILE_TYPE		= 4,
+	DIE_TYPE		= 5,
+	DIEGRP_TYPE		= 6,
+	MAX_TYPE_1F		= 7,
+};
+
+/*
+ * Use a lookup table for the case that there are future types > 6 which
+ * describe an intermediate domain level which does not exist today.
+ */
+static const unsigned int topo_domain_map_0b_1f[MAX_TYPE_1F] = {
+	[SMT_TYPE]	= TOPO_SMT_DOMAIN,
+	[CORE_TYPE]	= TOPO_CORE_DOMAIN,
+	[MODULE_TYPE]	= TOPO_MODULE_DOMAIN,
+	[TILE_TYPE]	= TOPO_TILE_DOMAIN,
+	[DIE_TYPE]	= TOPO_DIE_DOMAIN,
+	[DIEGRP_TYPE]	= TOPO_DIEGRP_DOMAIN,
+};
+
+static inline bool topo_subleaf(struct topo_scan *tscan, u32 leaf, u32 subleaf,
+				unsigned int *last_dom)
+{
+	unsigned int dom, maxtype;
+	const unsigned int *map;
+	struct {
+		// eax
+		u32	x2apic_shift	:  5, // Number of bits to shift APIC ID right
+					      // for the topology ID at the next level
+					: 27; // Reserved
+		// ebx
+		u32	num_processors	: 16, // Number of processors at current level
+					: 16; // Reserved
+		// ecx
+		u32	level		:  8, // Current topology level. Same as sub leaf number
+			type		:  8, // Level type. If 0, invalid
+					: 16; // Reserved
+		// edx
+		u32	x2apic_id	: 32; // X2APIC ID of the current logical processor
+	} sl;
+
+	switch (leaf) {
+	case 0x0b: maxtype = MAX_TYPE_0B; map = topo_domain_map_0b_1f; break;
+	case 0x1f: maxtype = MAX_TYPE_1F; map = topo_domain_map_0b_1f; break;
+	default: return false;
+	}
+
+	cpuid_subleaf(leaf, subleaf, &sl);
+
+	if (!sl.num_processors || sl.type == INVALID_TYPE)
+		return false;
+
+	if (sl.type >= maxtype) {
+		pr_err_once("Topology: leaf 0x%x:%d Unknown domain type %u\n",
+			    leaf, subleaf, sl.type);
+		/*
+		 * It really would have been too obvious to make the domain
+		 * type space sparse and leave a few reserved types between
+		 * the points which might change instead of following the
+		 * usual "this can be fixed in software" principle.
+		 */
+		dom = *last_dom + 1;
+	} else {
+		dom = map[sl.type];
+		*last_dom = dom;
+	}
+
+	if (!dom) {
+		tscan->c->topo.initial_apicid = sl.x2apic_id;
+	} else if (tscan->c->topo.initial_apicid != sl.x2apic_id) {
+		pr_warn_once(FW_BUG "CPUID leaf 0x%x subleaf %d APIC ID mismatch %x != %x\n",
+			     leaf, subleaf, tscan->c->topo.initial_apicid, sl.x2apic_id);
+	}
+
+	topology_set_dom(tscan, dom, sl.x2apic_shift, sl.num_processors);
+	return true;
+}
+
+static bool parse_topology_leaf(struct topo_scan *tscan, u32 leaf)
+{
+	unsigned int last_dom;
+	u32 subleaf;
+
+	/* Read all available subleafs and populate the levels */
+	for (subleaf = 0, last_dom = 0; topo_subleaf(tscan, leaf, subleaf, &last_dom); subleaf++);
+
+	/* If subleaf 0 failed to parse, give up */
+	if (!subleaf)
+		return false;
+
+	/*
+	 * There are machines in the wild which have shift 0 in the subleaf
+	 * 0, but advertise 2 logical processors at that level. They are
+	 * truly SMT.
+	 */
+	if (!tscan->dom_shifts[TOPO_SMT_DOMAIN] && tscan->dom_ncpus[TOPO_SMT_DOMAIN] > 1) {
+		unsigned int sft = get_count_order(tscan->dom_ncpus[TOPO_SMT_DOMAIN]);
+
+		pr_warn_once(FW_BUG "CPUID leaf 0x%x subleaf 0 has shift level 0 but %u CPUs. Fixing it up.\n",
+			     leaf, tscan->dom_ncpus[TOPO_SMT_DOMAIN]);
+		topology_update_dom(tscan, TOPO_SMT_DOMAIN, sft, tscan->dom_ncpus[TOPO_SMT_DOMAIN]);
+	}
+
+	set_cpu_cap(tscan->c, X86_FEATURE_XTOPOLOGY);
+	return true;
+}
+
+bool cpu_parse_topology_ext(struct topo_scan *tscan)
+{
+	/* Intel: Try leaf 0x1F first. */
+	if (tscan->c->cpuid_level >= 0x1f && parse_topology_leaf(tscan, 0x1f))
+		return true;
+
+	/* Intel/AMD: Fall back to leaf 0xB if available */
+	return tscan->c->cpuid_level >= 0x0b && parse_topology_leaf(tscan, 0x0b);
+}