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Date:   Wed,  3 Jul 2019 10:23:55 +0800
From:   Zhenzhong Duan <>
Cc:     Zhenzhong Duan <>,
        "K. Y. Srinivasan" <>,
        Haiyang Zhang <>,
        Stephen Hemminger <>,
        Sasha Levin <>,
        Juergen Gross <>,
        Boris Ostrovsky <>,
        Peter Zijlstra <>,
        Waiman Long <>,
        Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,
Subject: [PATCH v3] locking/spinlocks, paravirt, hyperv: Correct the hv_nopvspin case

With the boot parameter "hv_nopvspin" specified a Hyperv guest should
not make use of paravirt spinlocks, but behave as if running on bare
metal. This is not true, however, as the qspinlock code will fall back
to a test-and-set scheme when it is detecting a hypervisor.

In order to avoid this disable the virt_spin_lock_key.

Same change for XEN is already in Commit e6fd28eb3522
("locking/spinlocks, paravirt, xen: Correct the xen_nopvspin case")

Signed-off-by: Zhenzhong Duan <>
Cc: "K. Y. Srinivasan" <>
Cc: Haiyang Zhang <>
Cc: Stephen Hemminger <>
Cc: Sasha Levin <>
Cc: Juergen Gross <>
Cc: Boris Ostrovsky <>
Cc: Peter Zijlstra <>
Cc: Waiman Long <>
Cc: Thomas Gleixner <>
Cc: Ingo Molnar <>
Cc: Borislav Petkov <>
v3: remove unlikely() as suggested by Sasha

 arch/x86/hyperv/hv_spinlock.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
index 07f21a0..210495b 100644
--- a/arch/x86/hyperv/hv_spinlock.c
+++ b/arch/x86/hyperv/hv_spinlock.c
@@ -64,6 +64,9 @@ __visible bool hv_vcpu_is_preempted(int vcpu)
 void __init hv_init_spinlocks(void)
+	if (!hv_pvspin)
+		static_branch_disable(&virt_spin_lock_key);
 	if (!hv_pvspin || !apic ||
 	    !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
 	    !(ms_hyperv.features & HV_X64_MSR_GUEST_IDLE_AVAILABLE)) {

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