Re: [PATCH v10 098/108] KVM: TDX: Implement callbacks for MSR operations for TDX

[Ackerley Tng]

I believe we should also have a handler for .msr_filter_changed.

Without an .msr_filter_changed handler, a host crash can occur if we
first set up a vcpu for the TD, and then set an MSR filter.

If we first set up a vcpu for the TD, and then set an MSR filter, upon
vcpu_enter_guest, the .msr_filter_changed handler (currently
vmx_msr_filter_changed()) will be invoked. to_vmx(vcpu) interprets the
containing struct of struct kvm_vcpu to be a struct vcpu_vmx instead of
a struct vcpu_tdx.

In my case, I was working on a selftest and the missing handler caused a
NULL dereference in vmx_disable_intercept_for_msr() because
vmx->vmcs01.msr_bitmap is NULL.