Re: [kvm-unit-tests PATCH v3 2/2] x86/vmx: (Re)Add a nVMX test to validate load/save of DEBUGCTL

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 5/27/2026 11:12 PM, Sean Christopherson wrote:
> From: Chenyi Qiang <chenyi.qiang@intel.com>
> 
> Add a nVMX test to verify that DEBUGCTL is/isn't loaded/saved on entry/exit
> as per vmcs12's controls.  Validate all combinations of legal values (only
> three bits are supported, i.e. there are only 8 unique combinations), for
> both the host and the guest, along with '0'.
> 
> Validate that:
> 
>   - DEBUGCTL is loaded from vmcs.GUEST_DEBUGCTL iff "Load debug controls"
>     is set, otherwise the guest should see the host's value.
>   - DEBUGCTL is saved to vmcs.GUEST_DEBUGCTL iff "Save debug controls" is
>     set, otherwise the VMCS should retain its previous value.
>   - DEBUGCTL is *always* zeroed on VM-Exit, irrespective of guest controls.
> 
> Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
> Co-developed-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> +static void __vmx_debugctl_test(u64 host_val, u64 guest_val)
> +{
> +	u64 val, rand;
> +
> +	/* Validate VM-Entrywhen save/load debug controls are set */

missing a space between "VM-Entry" and "when".

But I don't understand why we need such a comment at all. Does it 
explain the purpose of following vmcs write is to validate that the two 
vmcs bits are allowed/supported on VM-Entry?

> +	vmcs_set_bits(ENT_CONTROLS, ENT_LOAD_DBGCTLS);
> +	vmcs_set_bits(EXI_CONTROLS, EXI_SAVE_DBGCTLS);