On Thu, Oct 19, 2023 at 03:48:48PM +1100, Michael Ellerman wrote:

Srikar Dronamraju [off-list ref] writes:

quoted

Like L2-cache info, coregroup information which is used to determine MC
sched domains is only present on dedicated LPARs. i.e PowerVM doesn't
export coregroup information for shared processor LPARs. Hence disable
creating MC domains on shared LPAR Systems.

Signed-off-by: Srikar Dronamraju <redacted>
---
 arch/powerpc/kernel/smp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 498c2d51fc20..29da9262cb17 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c

@@ -1046,6 +1046,10 @@ static struct cpumask *cpu_coregroup_mask(int cpu)
 
 static bool has_coregroup_support(void)
 {
+	/* Coregroup identification not available on shared systems */
+	if (is_shared_processor())
+		return 0;

That will catch guests running under KVM too right? Do we want that?

Some KVM people use vcpu pinning and pass-through topology things,
slice-of-hardware or something like that. In that scenario you actively
do want this.

I'm fairly clueless on when this is_shared_processor() gets to be true,
so that might already be dealt with..