On 4/1/25 11:10, Paolo Bonzini wrote: > For userspace to have fun with planes it is probably useful to let them > create vCPUs on the non-zero planes as well. Since such vCPUs are backed > by the same struct kvm_vcpu, these are regular vCPU file descriptors except > that they only allow a small subset of ioctls (mostly get/set) and they > share some of the backing resources, notably vcpu->run. > > TODO: prefault might be useful on non-default planes as well? > > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > --- > Documentation/virt/kvm/locking.rst | 3 + > include/linux/kvm_host.h | 4 +- > include/uapi/linux/kvm.h | 1 + > virt/kvm/kvm_main.c | 167 +++++++++++++++++++++++------ > 4 files changed, 142 insertions(+), 33 deletions(-) > > @@ -4200,8 +4223,13 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id) > * release semantics, which ensures the write is visible to kvm_get_vcpu(). > */ > vcpu->plane = -1; > - vcpu->vcpu_idx = atomic_read(&kvm->online_vcpus); > - r = xa_insert(&kvm->planes[0]->vcpu_array, vcpu->vcpu_idx, vcpu, GFP_KERNEL_ACCOUNT); > + if (plane->plane) > + vcpu->vcpu_idx = atomic_read(&kvm->online_vcpus); > + else > + vcpu->vcpu_idx = plane0_vcpu->vcpu_idx; Don't you want the atomic_read() for the plane0 vCPU and use the plane0 vcpu->idx value for non-zero plane vCPUs? > + > + r = xa_insert(&plane->vcpu_array, vcpu->vcpu_idx, > + vcpu, GFP_KERNEL_ACCOUNT); > WARN_ON_ONCE(r == -EBUSY); > if (r) > goto unlock_vcpu_destroy; > @@ -4220,13 +4248,14 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id) > if (r < 0) > goto kvm_put_xa_erase; > > - atomic_inc(&kvm->online_vcpus); > + if (!plane0_vcpu) It looks like plane0_vcpu will always have value, either from input or assigned in an else path earlier in the code. Should this be "!plane->plane" ? Thanks, Tom > + atomic_inc(&kvm->online_vcpus);
