Merge tag 'x86-urgent-2025-09-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Ingo Molnar:
 "Fix a CPU topology code regression that caused the mishandling of
  certain boot command line options, and re-enable CONFIG_PTDUMP on i386
  that was mistakenly turned off in the Kconfig"

* tag 'x86-urgent-2025-09-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/topology: Implement topology_is_core_online() to address SMT regression
  x86/Kconfig: Reenable PTDUMP on i386

Author: torvalds

arch/x86/Kconfig

@@ -26,7 +26,6 @@ config X86_64
 	depends on 64BIT
 	# Options that are inherently 64-bit kernel only:
 	select ARCH_HAS_GIGANTIC_PAGE
-	select ARCH_HAS_PTDUMP
 	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
 	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
 	select ARCH_SUPPORTS_PER_VMA_LOCK
@@ -99,6 +98,7 @@ config X86
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	select ARCH_HAS_PMEM_API		if X86_64
 	select ARCH_HAS_PREEMPT_LAZY
+	select ARCH_HAS_PTDUMP
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_HW_PTE_YOUNG
 	select ARCH_HAS_NONLEAF_PMD_YOUNG	if PGTABLE_LEVELS > 2

arch/x86/include/asm/topology.h

@@ -231,6 +231,16 @@ static inline bool topology_is_primary_thread(unsigned int cpu)
 }
 #define topology_is_primary_thread topology_is_primary_thread
 
+int topology_get_primary_thread(unsigned int cpu);
+
+static inline bool topology_is_core_online(unsigned int cpu)
+{
+	int pcpu = topology_get_primary_thread(cpu);
+
+	return pcpu >= 0 ? cpu_online(pcpu) : false;
+}
+#define topology_is_core_online topology_is_core_online
+
 #else /* CONFIG_SMP */
 static inline int topology_phys_to_logical_pkg(unsigned int pkg) { return 0; }
 static inline int topology_max_smt_threads(void) { return 1; }

arch/x86/kernel/cpu/topology.c

@@ -372,6 +372,19 @@ unsigned int topology_unit_count(u32 apicid, enum x86_topology_domains which_uni
 	return topo_unit_count(lvlid, at_level, apic_maps[which_units].map);
 }
 
+#ifdef CONFIG_SMP
+int topology_get_primary_thread(unsigned int cpu)
+{
+	u32 apic_id = cpuid_to_apicid[cpu];
+
+	/*
+	 * Get the core domain level APIC id, which is the primary thread
+	 * and return the CPU number assigned to it.
+	 */
+	return topo_lookup_cpuid(topo_apicid(apic_id, TOPO_CORE_DOMAIN));
+}
+#endif
+
 #ifdef CONFIG_ACPI_HOTPLUG_CPU
 /**
  * topology_hotplug_apic - Handle a physical hotplugged APIC after boot