[PATCH 8/9] powerpc: Add HOTPLUG_SMT support

Michael Ellerman
2023-05-24T16:00:20Z

Add support for HOTPLUG_SMT, which enables the generic sysfs SMT support
files in /sys/devices/system/cpu/smt, as well as the "nosmt" boot
parameter.

Implement the recently added hooks to allow partial SMT states, allow
any number of threads per core.

Tie the config symbol to HOTPLUG_CPU, which enables it on the major
platforms that support SMT. If there are other platforms that want the
SMT support that can be tweaked in future.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/topology.h | 25 +++++++++++++++++++++++++
arch/powerpc/kernel/smp.c | 3 +++
3 files changed, 29 insertions(+)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 539d1f03ff42..5cf87ca10a9c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -273,6 +273,7 @@ config PPC
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_VIRT_CPU_ACCOUNTING
select HAVE_VIRT_CPU_ACCOUNTING_GEN
+ select HOTPLUG_SMT if HOTPLUG_CPU
select HUGETLB_PAGE_SIZE_VARIABLE if PPC_BOOK3S_64 && HUGETLB_PAGE
select IOMMU_HELPER if PPC64
select IRQ_DOMAIN
diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index 8a4d4f4d9749..1e9117a22d14 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -143,5 +143,30 @@ static inline int cpu_to_coregroup_id(int cpu)
#endif
#endif

+#ifdef CONFIG_HOTPLUG_SMT
+#include <linux/cpu_smt.h>
+#include <asm/cputhreads.h>
+
+static inline bool topology_smt_supported(void)
+{
+ return threads_per_core > 1;
+}
+
+static inline bool topology_smt_threads_supported(unsigned int num_threads)
+{
+ return num_threads <= threads_per_core;
+}
+
+static inline bool topology_is_primary_thread(unsigned int cpu)
+{
+ return cpu == cpu_first_thread_sibling(cpu);
+}
+
+static inline bool topology_smt_thread_allowed(unsigned int cpu)
+{
+ return cpu_thread_in_core(cpu) < cpu_smt_num_threads;
+}
+#endif
+
#endif /* __KERNEL__ */
#endif /* _ASM_POWERPC_TOPOLOGY_H */
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 265801a3e94c..eed20b9253b7 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1154,6 +1154,9 @@ void __init smp_prepare_cpus(unsigned int max_cpus)

if (smp_ops && smp_ops->probe)
smp_ops->probe();
+
+ // Initalise the generic SMT topology support
+ cpu_smt_check_topology(threads_per_core);
}

void smp_prepare_boot_cpu(void)
--
2.40.1