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

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Message-ID: <20181105141128.GB24038@linux.intel.com>
Date:   Mon, 5 Nov 2018 16:11:28 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-sgx@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        sean.j.christopherson@...el.com, nhorman@...hat.com,
        npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, haitao.huang@...el.com,
        mark.shanahan@...el.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        David Woodhouse <dwmw@...zon.co.uk>, davidwang@...oxin.com,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>,
        qianyue.zj@...baba-inc.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v15 05/23] x86/cpu/intel: Detect SGX support and update
 caps appropriately

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