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Found one x2apic pre-enabled system, x2apic_mode suddenly get corrupted after register some cpus, when compiled CONFIG_NR_CPUS=255 instead of 512. It turns out that generic_processor_info() ==> phyid_set(apicid, phys_cpu_present_map) causes the problem. phys_cpu_present_map is sized by MAX_APICS bits, and pre-enabled system some cpus have an apic id > 255. The variable after phys_cpu_present_map may get corrupted silently: ffffffff828e8420 B phys_cpu_present_map ffffffff828e8440 B apic_verbosity ffffffff828e8444 B local_apic_timer_c2_ok ffffffff828e8448 B disable_apic ffffffff828e844c B x2apic_mode ffffffff828e8450 B x2apic_disabled ffffffff828e8454 B num_processors ... Actually phys_cpu_present_map is referenced via apic id, instead index. We should use MAX_LOCAL_APIC instead MAX_APICS. For 64-bit it will be 32768 in all cases. BSS will increase by 4k bytes on 64-bit: text data bss dec filename 21696943 4193748 12787712 38678403 vmlinux.before 21696943 4193748 12791808 38682499 vmlinux.after No change on 32bit. Finally we can remove MAX_APCIS that was rather confusing. Signed-off-by: Yinghai Lu <yinghai@kernel.org> Cc: H. Peter Anvin <hpa@linux.intel.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> LKML-Reference: <4D23BD9C.3070102@kernel.org> Signed-off-by: Ingo Molnar <mingo@elte.hu> |
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