x86/smp: Provide topology_is_primary_thread()

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If the CPU is supporting SMT then the primary thread can be found by
checking the lower APIC ID bits for zero. smp_num_siblings is used to build
the mask for the APIC ID bits which need to be taken into account.

This uses the MPTABLE or ACPI/MADT supplied APIC ID, which can be different
than the initial APIC ID in CPUID. But according to AMD the lower bits have
to be consistent. Intel gave a tentative confirmation as well.

Preparatory patch to support disabling SMT at boot/runtime.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Ingo Molnar <mingo@kernel.org>

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This commit is contained in:

Thomas Gleixner 2018-05-29 17:50:22 +02:00

parent ba2591a599

commit 6a4d2657e0

4 changed files with 33 additions and 1 deletions

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6

arch/x86/include/asm/apic.h

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4

arch/x86/include/asm/topology.h

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15

arch/x86/kernel/apic/apic.c

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9

arch/x86/kernel/smpboot.c

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