x86/smp: Provide topology_is_primary_thread()
commit 6a4d2657e048f096c7ffcad254010bd94891c8c0 upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
4 files changed
