KVM: init bsp_vcpu before kvm_arch_vcpu_init

On x86 mp_state is initialized by kvm_arch_vcpu_init. Right now kvm_vcpu_is_bsp returns false because kvm->bsp_vcpu has not been initialized, so vcpu_id == 0 ends up with mp_state == KVM_MP_STATE_UNINITIALIZED.

Gleb do you see a better way to fix this?

Signed-off-by Marcelo Tosatti <[email protected]>

virt/kvm/kvm_main.c +7 -3

index 8939ffa..7225064 100644
@@ -773,6 +773,13 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
 	struct page *page;
 	int r;
 
+	mutex_lock(&kvm->lock);
+#ifdef CONFIG_KVM_APIC_ARCHITECTURE
+	if (kvm->bsp_vcpu_id == id)
+		kvm->bsp_vcpu = vcpu;
+#endif
+	mutex_unlock(&kvm->lock);
+
 	mutex_init(&vcpu->mutex);
 	vcpu->cpu = -1;
 	vcpu->kvm = kvm;

@@ -1760,14 +1767,12 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 	smp_wmb();
 	atomic_inc(&kvm->online_vcpus);
 
-#ifdef CONFIG_KVM_APIC_ARCHITECTURE
-	if (kvm->bsp_vcpu_id == id)
-		kvm->bsp_vcpu = vcpu;

Quoted 8 lines · Marcelo Tosatti

On x86 mp_state is initialized by kvm_arch_vcpu_init. Right now kvm_vcpu_is_bsp returns false because kvm->bsp_vcpu has not been initialized, so vcpu_id == 0 ends up with mp_state == KVM_MP_STATE_UNINITIALIZED.

Gleb do you see a better way to fix this?

I have two, not necessary better ways. The first one is to change kvm_vcpu_is_bsp() to do kvm->bsp_vcpu_id == vcpu->vcpu_id.

Another one is to understand why mp_state is set to runnable for bsp here at all. May be we can drop this use of kvm_vcpu_is_bsp() since mp_state will be set to RUNNABLE in kvm_arch_vcpu_ioctl_set_sregs() anyway?

Quoted 11 lines · Gleb Natapov

Quoted 8 lines · Marcelo Tosatti

On x86 mp_state is initialized by kvm_arch_vcpu_init. Right now kvm_vcpu_is_bsp returns false because kvm->bsp_vcpu has not been initialized, so vcpu_id == 0 ends up with mp_state == KVM_MP_STATE_UNINITIALIZED.

Gleb do you see a better way to fix this?

I have two, not necessary better ways. The first one is to change kvm_vcpu_is_bsp() to do kvm->bsp_vcpu_id == vcpu->vcpu_id.

Thats much better.

Quoted 4 lines

Another one is to understand why mp_state is set to runnable for bsp here at all. May be we can drop this use of kvm_vcpu_is_bsp() since mp_state will be set to RUNNABLE in kvm_arch_vcpu_ioctl_set_sregs() anyway?

Testcase is kvmctl without -p, which does not do kvm_arch_vcpu_ioctl_set_sregs. I suppose that is valid? (in practice its no big deal since kvmctl can be updated, and qemu-kvm does set_sregs, but..).

KVM: use vcpu_id instead of bsp_vcpu pointer in kvm_vcpu_is_bsp

Change kvm_vcpu_is_bsp to use vcpu_id instead of bsp_vcpu pointer, which is only initialized at the end of kvm_vm_ioctl_create_vcpu.

Signed-off-by Marcelo Tosatti <[email protected]>

include/linux/kvm_host.h +0 -0

index 1b48092..026ed0a 100644

KVM: use vcpu_id instead of bsp_vcpu pointer in kvm_vcpu_is_bsp Change kvm_vcpu_is_bsp to use vcpu_id instead of bsp_vcpu pointer, which is only initialized at the end of kvm_vm_ioctl_create_vcpu.