Use largest APIC number, not number of CPUs to decide on physflat mode Handles case where BIOS gives CPUs very large APIC numbers correctly. Signed-off-by: Andi Kleen Index: linux/arch/x86_64/kernel/genapic.c =================================================================== --- linux.orig/arch/x86_64/kernel/genapic.c +++ linux/arch/x86_64/kernel/genapic.c @@ -45,7 +45,7 @@ void __init clustered_apic_check(void) u8 clusters, max_cluster; u8 id; u8 cluster_cnt[NUM_APIC_CLUSTERS]; - int num_cpus = 0; + int max_apic = 0; #if defined(CONFIG_ACPI) /* @@ -64,7 +64,8 @@ void __init clustered_apic_check(void) id = bios_cpu_apicid[i]; if (id == BAD_APICID) continue; - num_cpus++; + if (id > max_apic) + max_apic = id; cluster_cnt[APIC_CLUSTERID(id)]++; } @@ -79,7 +80,7 @@ void __init clustered_apic_check(void) we have ACPI platform support for CPU hotplug we should detect hotplug capablity from ACPI tables and only do this when really needed. -AK */ - if (num_cpus <= 8) + if (max_apic <= 8) genapic = &apic_flat; #endif goto print;