RISC-V: Enable HOTPLUG_PARALLEL for secondary CPUs

The core kernel already supports parallel bringup of secondary
CPUs (aka HOTPLUG_PARALLEL). The x86 and MIPS architectures
already use HOTPLUG_PARALLEL and ARM is also moving toward it.

On RISC-V, there is no arch specific global data accessed in the
RISC-V secondary CPU bringup path so enabling HOTPLUG_PARALLEL for
RISC-V would only require:
1) Providing RISC-V specific arch_cpuhp_kick_ap_alive()
2) Calling cpuhp_ap_sync_alive() from smp_callin()

This patch is tested natively with OpenSBI on QEMU RV64 virt machine
with 64 cores and also tested with KVM RISC-V guest with 32 VCPUs.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://patch.msgid.link/20250905122512.71684-1-apatel@ventanamicro.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index fadec20b87a8e3ef97bed64270e496ddb45244ac..34c68bb3b85710f16228256ed0ff8179cf37b180 100644 (file)
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -198,7 +198,7 @@ config RISCV
        select HAVE_SAMPLE_FTRACE_DIRECT_MULTI
        select HAVE_STACKPROTECTOR
        select HAVE_SYSCALL_TRACEPOINTS
-       select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
+       select HOTPLUG_PARALLEL if HOTPLUG_CPU
        select IRQ_DOMAIN
        select IRQ_FORCED_THREADING
        select KASAN_VMALLOC if KASAN

diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index 601a321e0f176465835248a76232876db42f48bc..d85916a3660c3a2704b3d67fa55ba768971c8b10 100644 (file)
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -39,7 +39,9 @@
 
 #include "head.h"
 
+#ifndef CONFIG_HOTPLUG_PARALLEL
 static DECLARE_COMPLETION(cpu_running);
+#endif
 
 void __init smp_prepare_cpus(unsigned int max_cpus)
 {
@@ -179,6 +181,12 @@ static int start_secondary_cpu(int cpu, struct task_struct *tidle)
        return -EOPNOTSUPP;
 }
 
+#ifdef CONFIG_HOTPLUG_PARALLEL
+int arch_cpuhp_kick_ap_alive(unsigned int cpu, struct task_struct *tidle)
+{
+       return start_secondary_cpu(cpu, tidle);
+}
+#else
 int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 {
        int ret = 0;
@@ -199,6 +207,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 
        return ret;
 }
+#endif
 
 void __init smp_cpus_done(unsigned int max_cpus)
 {
@@ -225,6 +234,10 @@ asmlinkage __visible void smp_callin(void)
        mmgrab(mm);
        current->active_mm = mm;
 
+#ifdef CONFIG_HOTPLUG_PARALLEL
+       cpuhp_ap_sync_alive();
+#endif
+
        store_cpu_topology(curr_cpuid);
        notify_cpu_starting(curr_cpuid);
 
@@ -243,7 +256,9 @@ asmlinkage __visible void smp_callin(void)
         */
        local_flush_icache_all();
        local_flush_tlb_all();
+#ifndef CONFIG_HOTPLUG_PARALLEL
        complete(&cpu_running);
+#endif
        /*
         * Disable preemption before enabling interrupts, so we don't try to
         * schedule a CPU that hasn't actually started yet.