Re: [PATCH v24 07/24] x86/cpu/intel: Detect SGX supprt

From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	linux-sgx@vger.kernel.org, akpm@linux-foundation.org,
	dave.hansen@intel.com, sean.j.christopherson@intel.com,
	nhorman@redhat.com, npmccallum@redhat.com, serge.ayoun@intel.com,
	shay.katz-zamir@intel.com, haitao.huang@intel.com,
	andriy.shevchenko@linux.intel.com, tglx@linutronix.de,
	kai.svahn@intel.com, josh@joshtriplett.org, luto@kernel.org,
	kai.huang@intel.com, rientjes@google.com, cedric.xing@intel.com,
	puiterwijk@redhat.com
Subject: Re: [PATCH v24 07/24] x86/cpu/intel: Detect SGX supprt
Date: Thu, 19 Dec 2019 02:42:20 +0200	[thread overview]
Message-ID: <c956ba52a9f0b54cd8ab3ec034246662e792ac14.camel@linux.intel.com> (raw)
In-Reply-To: <20191217151744.GG28788@zn.tnic>

On Tue, 2019-12-17 at 16:17 +0100, Borislav Petkov wrote:
> On Sat, Nov 30, 2019 at 01:13:09AM +0200, Jarkko Sakkinen wrote:
> 
> Typo in the subject:
> 
> Subject: Re: [PATCH v24 07/24] x86/cpu/intel: Detect SGX supprt
> 							 ^^^^^^
> > From: Sean Christopherson <sean.j.christopherson@intel.com>
> > 
> > When the CPU supports SGX, check that the BIOS has enabled SGX and SGX1
> > opcodes are available. Otherwise, all the SGX related capabilities.
> > 
> > In addition, clear X86_FEATURE_SGX_LC also in the case when the launch
> > enclave are read-only. This way the feature bit reflects the level that
> > Linux supports the launch control.
> > 
> > The check is done for every CPU, not just BSP, in order to verify that
> > MSR_IA32_FEATURE_CONTROL is correctly configured on all CPUs. The other
> > parts of the kernel, like the enclave driver, expect the same
> > configuration from all CPUs.
> > 
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > Co-developed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> > ---
> >  arch/x86/kernel/cpu/intel.c | 41 +++++++++++++++++++++++++++++++++++++
> >  1 file changed, 41 insertions(+)
> 
> ...
> 
> > @@ -761,6 +797,11 @@ static void init_intel(struct cpuinfo_x86 *c)
> >  	if (cpu_has(c, X86_FEATURE_TME))
> >  		detect_tme(c);
> >  
> > +#ifdef CONFIG_INTEL_SGX
> > +	if (cpu_has(c, X86_FEATURE_SGX))
> > +		detect_sgx(c);
> > +#endif
> 
> You can remove the ifdeffery here and put the ifdef around the function
> body and drop the __maybe_unused tag:

OK, so I remember getting feedback on some unrelated to SGX stuff
that I should use __maybe_unused in the past. That is why I used
it here instead of ifdeffery.

It is used in bunch of places in the kernel. I'm a bit confused
when using it is a right thing and when it should be avoided.

/Jarkko