[PATCH] KVM: x86: take slots_lock in kvm_free_pit

From: Radim KrÄmÃÅ
Date: Mon Jul 10 2017 - 14:54:37 EST

kvm_vm_release() did not have slots_lock when calling
kvm_io_bus_unregister_dev() and this went unnoticed until 4a12f9517728
("KVM: mark kvm->busses as rcu protected") added dynamic checks.
Luckily, there should be no race at that point:

WARNING: suspicious RCU usage
4.12.0.kvm+ #0 Not tainted
./include/linux/kvm_host.h:479 suspicious rcu_dereference_check() usage!

kvm_io_bus_unregister_dev+0x173/0x190 [kvm]
kvm_free_pit+0x28/0x80 [kvm]
kvm_arch_sync_events+0x2d/0x30 [kvm]
kvm_put_kvm+0xa7/0x2a0 [kvm]
kvm_vm_release+0x21/0x30 [kvm]

Signed-off-by: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
arch/x86/kvm/i8254.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index a78b445ce411..af192895b1fc 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -724,8 +724,10 @@ void kvm_free_pit(struct kvm *kvm)
struct kvm_pit *pit = kvm->arch.vpit;

if (pit) {
+ mutex_lock(&kvm->slots_lock);
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &pit->dev);
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &pit->speaker_dev);
+ mutex_unlock(&kvm->slots_lock);
kvm_pit_set_reinject(pit, false);