diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c index d17c9b71eb4a..621a151ccf7d 100644 --- a/arch/x86/kernel/cpu/topology.c +++ b/arch/x86/kernel/cpu/topology.c @@ -128,6 +128,9 @@ static void topo_set_cpuids(unsigned int cpu, u32 apic_id, u32 acpi_id) static __init bool check_for_real_bsp(u32 apic_id) { + bool is_bsp = false, has_apic_base = boot_cpu_data.x86 >= 6; + u64 msr; + /* * There is no real good way to detect whether this a kdump() * kernel, but except on the Voyager SMP monstrosity which is not @@ -144,17 +147,61 @@ static __init bool check_for_real_bsp(u32 apic_id) if (topo_info.real_bsp_apic_id != BAD_APICID) return false; - if (apic_id == topo_info.boot_cpu_apic_id) { - topo_info.real_bsp_apic_id = apic_id; - return false; + /* + * Check whether the enumeration order is broken by evaluating the + * BSP bit in the APICBASE MSR. If the CPU does not have the + * APICBASE MSR then the BSP detection is not possible and the + * kernel must rely on the firmware enumeration order. + */ + if (has_apic_base) { + rdmsrl(MSR_IA32_APICBASE, msr); + is_bsp = !!(msr & MSR_IA32_APICBASE_BSP); } - pr_warn("Boot CPU APIC ID not the first enumerated APIC ID: %x > %x\n", + if (apic_id == topo_info.boot_cpu_apic_id) { + /* + * If the boot CPU has the APIC BSP bit set then the + * firmware enumeration is agreeing. If the CPU does not + * have the APICBASE MSR then the only choice is to trust + * the enumeration order. + */ + if (is_bsp || !has_apic_base) { + topo_info.real_bsp_apic_id = apic_id; + return false; + } + /* + * If the boot APIC is enumerated first, but the APICBASE + * MSR does not have the BSP bit set, then there is no way + * to discover the real BSP here. Assume a crash kernel and + * limit the number of CPUs to 1 as an INIT to the real BSP + * would reset the machine. + */ + pr_warn("Enumerated BSP APIC %x is not marked in APICBASE MSR\n", apic_id); + pr_warn("Assuming crash kernel. Limiting to one CPU to prevent machine INIT\n"); + set_nr_cpu_ids(1); + goto fwbug; + } + + pr_warn("Boot CPU APIC ID not the first enumerated APIC ID: %x != %x\n", topo_info.boot_cpu_apic_id, apic_id); + + if (is_bsp) { + /* + * The boot CPU has the APIC BSP bit set. Use it and complain + * about the broken firmware enumeration. + */ + topo_info.real_bsp_apic_id = topo_info.boot_cpu_apic_id; + goto fwbug; + } + pr_warn("Crash kernel detected. Disabling real BSP to prevent machine INIT\n"); topo_info.real_bsp_apic_id = apic_id; return true; + +fwbug: + pr_warn(FW_BUG "APIC enumeration order not specification compliant\n"); + return false; } static unsigned int topo_unit_count(u32 lvlid, enum x86_topology_domains at_level,