releases/6.1.160/s390-smp-fix-fallback-cpu-detection.patch

From 0044965180ba15f1a5984d6eca19850afd7cb838 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Mon, 20 Oct 2025 16:17:54 +0200
Subject: s390/smp: Fix fallback CPU detection

From: Heiko Carstens <hca@linux.ibm.com>

[ Upstream commit 07a75d08cfa1b883a6e1256666e5f0617ee99231 ]

In case SCLP CPU detection does not work a fallback mechanism using SIGP is
in place. Since a cleanup this does not work correctly anymore: new CPUs
are only considered if their type matches the boot CPU.

Before the cleanup the information if a CPU type should be considered was
also part of a structure generated by the fallback mechanism and indicated
that a CPU type should not be considered when adding CPUs.

Since the rework a global SCLP state is used instead. If the global SCLP
state indicates that the CPU type should be considered and the fallback
mechanism is used, there may be a mismatch with CPU types if CPUs are
added. This can lead to a system with only a single CPU even tough there
are many more CPUs.

Address this by simply copying the boot cpu type into the generated data
structure from the fallback mechanism.

Reported-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Fixes: d08d94306e90 ("s390/smp: cleanup core vs. cpu in the SCLP interface")
Reviewed-by: Mete Durlu <meted@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/s390/kernel/smp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 436dbf4d743d8..8346cb75643ca 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -758,6 +758,7 @@ static void __ref smp_get_core_info(struct sclp_core_info *info, int early)
 				continue;
 			info->core[info->configured].core_id =
 				address >> smp_cpu_mt_shift;
+			info->core[info->configured].type = boot_core_type;
 			info->configured++;
 		}
 		info->combined = info->configured;
-- 
2.51.0