linux-kernel - [PATCH 1/2] KVM: X86: Fix setup the virt_spin_lock

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Date:   Sat, 24 Mar 2018 21:17:24 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 1/2] KVM: X86: Fix setup the virt_spin_lock_key before static key get initialized

From: Wanpeng Li <wanpengli@...cent.com>

 static_key_disable_cpuslocked(): static key 'virt_spin_lock_key+0x0/0x20' used before call to jump_label_init()
 WARNING: CPU: 0 PID: 0 at kernel/jump_label.c:161 static_key_disable_cpuslocked+0x61/0x80
 RIP: 0010:static_key_disable_cpuslocked+0x61/0x80
 Call Trace:
  static_key_disable+0x16/0x20
  start_kernel+0x192/0x4b3
  secondary_startup_64+0xa5/0xb0

Qspinlock will be choosed when dedicated pCPUs are available, however, the 
static virt_spin_lock_key is set in kvm_spinlock_init() before jump_label_init() 
has been called, which will result in a WARN(). This patch fixes it by delaying
the virt_spin_lock_key setup to .smp_prepare_cpus().

Reported-by: Davidlohr Bueso <dbueso@...e.de>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Davidlohr Bueso <dbueso@...e.de>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
Note: Peterz pointed out in the IRC we have to audit all the architectures that 
implement smp_prepare_boot_cpu() to see what they depend on if we want to move 
jump_label_init() before smp_prepare_boot_cpu(). So what this patch does is 
similar to the issue which handled in xen ca5d376e.

 arch/x86/kernel/kvm.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 4ccbff6..747c61b 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -454,6 +454,13 @@ static void __init sev_map_percpu_data(void)
 }
 
 #ifdef CONFIG_SMP
+static void __init kvm_smp_prepare_cpus(unsigned int max_cpus)
+{
+	native_smp_prepare_cpus(max_cpus);
+	if (kvm_para_has_hint(KVM_HINTS_DEDICATED))
+		static_branch_disable(&virt_spin_lock_key);
+}
+
 static void __init kvm_smp_prepare_boot_cpu(void)
 {
 	/*
@@ -557,6 +564,7 @@ static void __init kvm_guest_init(void)
 		kvm_setup_vsyscall_timeinfo();
 
 #ifdef CONFIG_SMP
+	smp_ops.smp_prepare_cpus = kvm_smp_prepare_cpus;
 	smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
 	if (cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "x86/kvm:online",
 				      kvm_cpu_online, kvm_cpu_down_prepare) < 0)
@@ -737,10 +745,8 @@ void __init kvm_spinlock_init(void)
 	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
 		return;
 
-	if (kvm_para_has_hint(KVM_HINTS_DEDICATED)) {
-		static_branch_disable(&virt_spin_lock_key);
+	if (kvm_para_has_hint(KVM_HINTS_DEDICATED))
 		return;
-	}
 
 	__pv_init_lock_hash();
 	pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
-- 
2.7.4