Re: [PATCH v4 07/11] KVM: Initialize a vCPU's index to '-1' while it's being created

[Philippe Mathieu-Daudé]

On 1/7/26 00:56, Sean Christopherson wrote:
> 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.
>
> Unwind the index back to -1 if inserting the vCPU into the array or adding
> the vCPU to the fd table fails, so that kvm_arch_vcpu_destroy() sees the
> vCPU as unreachable, i.e. so that teardown logic doesn't hit false positive
> lockdep assertions.  Opportunistically add a comment to call out that the
> "real" index needs to be set before making the vCPU visible to other tasks.
>
> 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@xxxxxxxxxx>
> ---
>   virt/kvm/kvm_main.c | 8 ++++++++
>   1 file changed, 8 insertions(+)

Reviewed-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxxxxxxxx>