[PATCH V10 12/19] RISC-V: paravirt: pvqspinlock: Add nopvspin kernel parameter

[guoren@kernel.org]

From: Guo Ren <guoren@linux.alibaba.com>

Disables the qspinlock slow path using PV optimizations which
allow the hypervisor to 'idle' the guest on lock contention.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  2 +-
 arch/riscv/kernel/paravirt.c                    | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index de6b7ee752cd..1a8878f6bfbd 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3820,7 +3820,7 @@
 			as generic guest with no PV drivers. Currently support
 			XEN HVM, KVM, HYPER_V and VMWARE guest.
 
-	nopvspin	[X86,XEN,KVM]
+	nopvspin	[X86,XEN,KVM,RISC-V]
 			Disables the qspinlock slow path using PV optimizations
 			which allow the hypervisor to 'idle' the guest on lock
 			contention.
diff --git a/arch/riscv/kernel/paravirt.c b/arch/riscv/kernel/paravirt.c
index 1bacb2cf3872..b55c3d3c0c17 100644
--- a/arch/riscv/kernel/paravirt.c
+++ b/arch/riscv/kernel/paravirt.c
@@ -165,8 +165,21 @@ DEFINE_STATIC_CALL(pv_queued_spin_unlock, native_queued_spin_unlock);
 EXPORT_SYMBOL(__SCK__pv_queued_spin_lock_slowpath);
 EXPORT_SYMBOL(__SCK__pv_queued_spin_unlock);
 
+static bool nopvspin;
+static __init int parse_nopvspin(char *arg)
+{
+       nopvspin = true;
+       return 0;
+}
+early_param("nopvspin", parse_nopvspin);
+
 void __init pv_qspinlock_init(void)
 {
+	if (nopvspin) {
+		pr_info("PV qspinlocks disabled\n");
+		return;
+	}
+
 	if (num_possible_cpus() == 1)
 		return;
 
-- 
2.36.1