RE: [PATCH v3 4/6] x86/gsseg: move local_irq_save/restore() into asm_load_gs_index()

H. Peter Anvin
2022-10-18T18:14:45Z

On October 18, 2022 10:25:31 AM PDT, "Li, Xin3" <xin3.li@intel.com> wrote:
>> > static inline void native_load_gs_index(unsigned int selector) {
>> > - unsigned long flags;
>> > -
>> > - local_irq_save(flags);
>> > asm_load_gs_index(selector);
>> > - local_irq_restore(flags);
>> > }
>>
>> static inline void native_load_gs_index(unsigned int selector) {
>> unsigned long flags;
>>
>> if (cpu_feature_enabled(LKGS)) {
>> native_lkgs(selector);
>> } else {
>> local_irq_save(flags);
>> asm_load_gs_index(selector);
>> local_irq_restore(flags);
>> }
>> }
>>
>> For paravirt enabled kernels we want during feature detection:
>>
>> if (cpu_feature_enabled(LKGS)))
>> pv_ops.cpu.load_gs_index = native_lkgs;
>
>If we use static_cpu_has in native_load_gs_index
> if (static_cpu_has(X86_FEATURE_LKGS)) {
> native_lkgs(selector);
> }
>
>We don't have to change pv_ops.cpu.load_gs_index, right?
>
>Thanks!
>Xin
>
>>
>> No?
>>
>> Thanks,
>>
>> tglx
>

You don't *have* to, but it would mean a branch to a branch, so it would be more efficient. It would strictly be an optimization.