From: Fernando Luis Vazquez Cao hard_smp_processor_id used to be just a macro that hard-coded hard_smp_processor_id to 0 in the non SMP case. When booting non SMP kernels on hardware where the boot ioapic id is not 0 this turns out to be a problem. This is happens frequently in the case of kdump and once in a great while in the case of real hardware. Use the APIC to determine the hardware processor id in both UP and SMP kernels to fix this issue. Notice that hard_smp_processor_id is only used by SMP code or by code that works with apics so we do not need to handle the case when apics are not present and hard_smp_processor_id should never be called there. Signed-off-by: Fernando Luis Vazquez Cao Cc: "Luck, Tony" Cc: Andi Kleen Cc: "Eric W. Biederman" Cc: Vivek Goyal Signed-off-by: Andrew Morton --- include/asm-x86_64/smp.h | 14 ++++++-------- 1 files changed, 6 insertions(+), 8 deletions(-) diff -puN include/asm-x86_64/smp.h~use-the-apic-to-determine-the-hardware-processor-id-x86_64 include/asm-x86_64/smp.h --- a/include/asm-x86_64/smp.h~use-the-apic-to-determine-the-hardware-processor-id-x86_64 +++ a/include/asm-x86_64/smp.h @@ -57,12 +57,6 @@ static inline int num_booting_cpus(void) #define raw_smp_processor_id() read_pda(cpunumber) -static inline int hard_smp_processor_id(void) -{ - /* we don't want to mark this access volatile - bad code generation */ - return GET_APIC_ID(*(unsigned int *)(APIC_BASE+APIC_ID)); -} - extern int __cpu_disable(void); extern void __cpu_die(unsigned int cpu); extern void prefill_possible_map(void); @@ -71,10 +65,14 @@ extern unsigned __cpuinitdata disabled_c #define NO_PROC_ID 0xFF /* No processor magic marker */ -#else /* CONFIG_SMP */ -#define hard_smp_processor_id() 0 #endif /* CONFIG_SMP */ +static inline int hard_smp_processor_id(void) +{ + /* we don't want to mark this access volatile - bad code generation */ + return GET_APIC_ID(*(unsigned int *)(APIC_BASE+APIC_ID)); +} + /* * Some lowlevel functions might want to know about * the real APIC ID <-> CPU # mapping. _