linux-kernel - [PATCH] RISC-V: Enable HOTPLUG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <20250905122512.71684-1-apatel@ventanamicro.com>
Date: Fri,  5 Sep 2025 17:55:12 +0530
From: Anup Patel <apatel@...tanamicro.com>
To: Palmer Dabbelt <palmer@...belt.com>,
	Paul Walmsley <paul.walmsley@...ive.com>
Cc: Alexandre Ghiti <alex@...ti.fr>,
	Sunil V L <sunilvl@...tanamicro.com>,
	Atish Patra <atish.patra@...ux.dev>,
	Andrew Jones <ajones@...tanamicro.com>,
	Anup Patel <anup@...infault.org>,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Anup Patel <apatel@...tanamicro.com>
Subject: [PATCH] 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 requires:
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@...tanamicro.com>
---
 arch/riscv/Kconfig          |  2 +-
 arch/riscv/kernel/smpboot.c | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index a4b233a0659e..d5800d6f9a15 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -196,7 +196,7 @@ 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 601a321e0f17..d85916a3660c 100644
--- 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.
-- 
2.43.0