KVM: x86: clean/fix memory barriers in irqchip_in_kernel

The memory barriers are trying to protect against concurrent RCU-based
interrupt injection, but the IRQ routing table is not valid at the time
kvm->arch.vpic is written.  Fix this by writing kvm->arch.vpic last.
kvm_destroy_pic then need not set kvm->arch.vpic to NULL; modify it
to take a struct kvm_pic* and reuse it if the IOAPIC creation fails.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 11 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2d62229aac26..23e47a0b054b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3626,30 +3626,25 @@ long kvm_arch_vm_ioctl(struct file *filp,
 			r = kvm_ioapic_init(kvm);
 			if (r) {
 				mutex_lock(&kvm->slots_lock);
-				kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
-							  &vpic->dev_master);
-				kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
-							  &vpic->dev_slave);
-				kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
-							  &vpic->dev_eclr);
+				kvm_destroy_pic(vpic);
 				mutex_unlock(&kvm->slots_lock);
-				kfree(vpic);
 				goto create_irqchip_unlock;
 			}
 		} else
 			goto create_irqchip_unlock;
-		smp_wmb();
-		kvm->arch.vpic = vpic;
-		smp_wmb();
 		r = kvm_setup_default_irq_routing(kvm);
 		if (r) {
 			mutex_lock(&kvm->slots_lock);
 			mutex_lock(&kvm->irq_lock);
 			kvm_ioapic_destroy(kvm);
-			kvm_destroy_pic(kvm);
+			kvm_destroy_pic(vpic);
 			mutex_unlock(&kvm->irq_lock);
 			mutex_unlock(&kvm->slots_lock);
+			goto create_irqchip_unlock;
 		}
+		/* Write kvm->irq_routing before kvm->arch.vpic.  */
+		smp_wmb();
+		kvm->arch.vpic = vpic;
 	create_irqchip_unlock:
 		mutex_unlock(&kvm->lock);
 		break;