Re: [PATCH v15 05/23] x86/cpu/intel: Detect SGX support and update caps appropriately

[Jarkko Sakkinen]

On Mon, Nov 05, 2018 at 04:09:33PM +0200, Jarkko Sakkinen wrote:
> On Sat, Nov 03, 2018 at 03:05:39PM +0200, Andy Shevchenko wrote:
> > > +static void detect_sgx(struct cpuinfo_x86 *c)
> > > +{
> > > +       bool unsupported = false;
> > > +       unsigned long long fc;
> > > +
> > > +       rdmsrl(MSR_IA32_FEATURE_CONTROL, fc);
> > > +       if (!(fc & FEATURE_CONTROL_LOCKED)) {
> > > +               pr_err_once("sgx: IA32_FEATURE_CONTROL MSR is not 
> > > locked\n");
> > > +               unsupported = true;
> > > +       } else if (!(fc & FEATURE_CONTROL_SGX_ENABLE)) {
> > > +               pr_err_once("sgx: not enabled in IA32_FEATURE_CONTROL 
> > > MSR\n");
> > > +               unsupported = true;
> > > +       } else if (!cpu_has(c, X86_FEATURE_SGX1)) {
> > > +               pr_err_once("sgx: SGX1 instruction set not supported\n");
> > > +               unsupported = true;
> > > +       }
> > 
> > If you do
> > 
> > } else {
> >  /* Supported */
> >  return;
> > }
> 
> Agree. Would this be a more clean flow in the attached patch?

Actually I'll paste the whole function for clarity because it is not too
long:

static void detect_sgx(struct cpuinfo_x86 *c)
{
        unsigned long long fc;

        rdmsrl(MSR_IA32_FEATURE_CONTROL, fc);
        if (!(fc & FEATURE_CONTROL_LOCKED)) {
                pr_err_once("sgx: IA32_FEATURE_CONTROL MSR is not locked\n");
                goto out_unsupported;
        }

        if (!(fc & FEATURE_CONTROL_SGX_ENABLE)) {
                pr_err_once("sgx: not enabled in IA32_FEATURE_CONTROL MSR\n");
                goto out_unsupported;
        }

        if (!cpu_has(c, X86_FEATURE_SGX1)) {
                pr_err_once("sgx: SGX1 instruction set not supported\n");
                goto out_unsupported;
        }

        if (!(fc & FEATURE_CONTROL_SGX_LE_WR)) {
                pr_info_once("sgx: launch control MSRs are not writable\n");
                goto out_msrs_rdonly;
        }

        return;
out_unsupported:
        setup_clear_cpu_cap(X86_FEATURE_SGX);
        setup_clear_cpu_cap(X86_FEATURE_SGX1);
        setup_clear_cpu_cap(X86_FEATURE_SGX2);
out_msrs_rdonly:
        setup_clear_cpu_cap(X86_FEATURE_SGX_LC);
}

/Jarkko