Re: [PATCH v3 09/18] x86/virt: KVM: Open code cpu_has_vmx() in KVM VMX

Huang, Kai
2023-05-23T00:25:01Z

On Fri, 2023-05-12 at 16:50 -0700, Sean Christopherson wrote:
> Fold the raw CPUID check for VMX into kvm_is_vmx_supported(), its sole
> user. Keep the check even though KVM also checks X86_FEATURE_VMX, as the
> intent is to provide a unique error message if VMX is unsupported by
> hardware, whereas X86_FEATURE_VMX may be clear due to firmware and/or
> kernel actions.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

To be honest I am not sure the benefit of open coding, but this is a simple
check, so:

Reviewed-by: Kai Huang <kai.huang@intel.com>

> ---
> arch/x86/include/asm/virtext.h | 10 ----------
> arch/x86/kvm/vmx/vmx.c | 2 +-
> 2 files changed, 1 insertion(+), 11 deletions(-)
>
> diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h
> index aaed66249ccf..b1171a5ad452 100644
> --- a/arch/x86/include/asm/virtext.h
> +++ b/arch/x86/include/asm/virtext.h
> @@ -22,14 +22,6 @@
> /*
> * VMX functions:
> */
> -
> -static inline int cpu_has_vmx(void)
> -{
> - unsigned long ecx = cpuid_ecx(1);
> - return test_bit(5, &ecx); /* CPUID.1:ECX.VMX[bit 5] -> VT */
> -}
> -
> -
> /**
> * cpu_vmxoff() - Disable VMX on the current CPU
> *
> @@ -61,8 +53,6 @@ static inline int cpu_vmx_enabled(void)
> }
>
> /** Disable VMX if it is enabled on the current CPU

Nit: looks the kdoc style comment (double **) can be removed.

> - *
> - * You shouldn't call this if cpu_has_vmx() returns 0.
> */
> static inline void __cpu_emergency_vmxoff(void)
> {
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 76cdb189f1b5..f44f93772b4f 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2721,7 +2721,7 @@ static bool kvm_is_vmx_supported(void)
> {
> int cpu = raw_smp_processor_id();
>
> - if (!cpu_has_vmx()) {
> + if (!(cpuid_ecx(1) & feature_bit(VMX))) {
> pr_err("VMX not supported by CPU %d\n", cpu);
> return false;
> }
> --
> 2.40.1.606.ga4b1b128d6-goog
>