[PATCH 1/2] KVM: X86: Fix setup the virt_spin_lock_key before static key get initialized

Wanpeng Li
2018-03-25T04:17:24Z

From: Wanpeng Li <wanpengli@tencent.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@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Wanpeng Li <wanpengli@tencent.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