On Wed, 31 Jul 2024 08:31:11 +0530, Nysal Jan K.A. wrote:

After the addition of HOTPLUG_SMT support for PowerPC [1] there was a
regression reported [2] when enabling SMT. On a system with at least
one offline core, when enabling SMT, the expectation is that no CPUs
of offline cores are made online.

On a POWER9 system with 4 cores in SMT4 mode:
$ ppc64_cpu --info
Core   0:    0*    1*    2*    3*
Core   1:    4*    5*    6*    7*
Core   2:    8*    9*   10*   11*
Core   3:   12*   13*   14*   15*

[...]

Applied to powerpc/fixes.

[1/2] cpu/SMT: Enable SMT only if a core is online
      https://git.kernel.org/powerpc/c/6c17ea1f3eaa330d445ac14a9428402ce4e3055e
[2/2] powerpc/topology: Check if a core is online
      https://git.kernel.org/powerpc/c/227bbaabe64b6f9cd98aa051454c1d4a194a8c6a

cheers