[PATCH v2 4/8] KVM: Initialize a vCPU's index to '-1' while it's being created

[Sean Christopherson <seanjc@google.com>]

Invalidate a vCPU's index immediately after allocating storage for the vCPU
so that KVM doesn't incorrectly treat a vCPU that is the process of being
created as being vCPU0.  This will also allow detecting that a vCPU is in
the process of being created and thus otherwise unreachable, which is
useful for avoiding false positives in lockdep assertions on vcpu->mutex.

Note, kvm_wait_for_vcpu_online() naturally does the right thing thanks to
vcpu->vcpu_idx and kvm->online_vcpus being signed values.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e44c20c04961..b3d2a678210c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4188,6 +4188,8 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id)
 		goto vcpu_decrement;
 	}
 
+	vcpu->vcpu_idx = -1;
+
 	BUILD_BUG_ON(sizeof(struct kvm_run) > PAGE_SIZE);
 	page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
 	if (!page) {
-- 
2.54.0.1136.gdb2ca164c4-goog