Re: [XEN][PATCH] x86/hvm: revise "cpu_has_vmx" usage for !CONFIG_INTEL_VMX case

[Jan Beulich <jbeulich@suse.com>]

On 24.09.2025 12:14, Grygorii Strashko wrote:
> From: Grygorii Strashko <grygorii_strashko@epam.com>
> 
> Since commit b99227347230 ("x86: Fix AMD_SVM and INTEL_VMX dependency") the
> HVM Intel VT-x support can be disabled, but it still keeps VMX
> code partially built-in. Particularly in HVM code there are two places:
> 
> 1) hvm/dom0_build.c
>  dom0_construct_pvh()->pvh_populate_p2m()
>     ...
>     if ( cpu_has_vmx && paging_mode_hap(d) && !vmx_unrestricted_guest(v) )
>     {
>         ...
>         [unreachable for !cpu_has_vmx case]
>         rc = pvh_setup_vmx_realmode_helpers(d);
> 
> pvh_setup_vmx_realmode_helpers() allocates memory and configures
>  HVM_PARAM_VM86_TSS_SIZED
>  HVM_PARAM_IDENT_PT
> 
> 2) hvm/hvm.c
>  hvm_set_param()
>     ...
>     case HVM_PARAM_IDENT_PT:
> 
>         if ( !paging_mode_hap(d) || !cpu_has_vmx )
>         {
>             d->arch.hvm.params[index] = value;
>             break;
>         }
>         [unreachable for !cpu_has_vmx case]
>         ...
> 
> Hence HVM_PARAM_IDENT_PT/HVM_PARAM_VM86_TSS_SIZED are used only by VMX code
> above code become unreachable in !cpu_has_vmx case and can be optimazed
> when !CONFIG_INTEL_VMX.
> 
> Replace "cpu_has_vmx" with using_vmx() to account !CONFIG_INTEL_VMX and allow
> compiler DCE to optimize code.
> 
> Signed-off-by: Grygorii Strashko <grygorii_strashko@epam.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>