Re: [PATCH v2 1/2] KVM: destruct kvm_io_device while unregistering it from kvm_io_bus

[Sean Christopherson]

On Tue, Feb 07, 2023, Wei Wang wrote:
> Current usage of kvm_io_device requires users to destruct it with an extra
> call of kvm_iodevice_destructor after the device gets unregistered from
> kvm_io_bus. This is not necessary and can cause errors if a user forgot
> to make the extra call.
> 
> Simplify the usage by combining kvm_iodevice_destructor into
> kvm_io_bus_unregister_dev. This reduces LOCs a bit for users and can
> avoid the leakage of destructing the device explicitly.

The changelog should really call out that coalesced_mmio_ops and ioeventfd_ops
are the only kvm_io_device_ops instances that implement ->destructor.  Without
that info, this change looks super dangerous as it's not obvious other paths won't
end up with a use-after-free.

Paolo, if/when you take this, can you tack on something like:

Note, coalesced_mmio_ops and ioeventfd_ops are the only instances of
kvm_io_device_ops that implement a destructor, all other callers of
kvm_io_bus_unregister_dev() are unaffected by this change.

> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
> ---

Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>