Re: [RFC PATCH v2 01/26] x86/cpufeatures: Add SGX1 and SGX2 sub-features

From: Kai Huang <kai.huang@intel.com>
To: Sean Christopherson <seanjc@google.com>, Borislav Petkov <bp@alien8.de>
Cc: linux-sgx@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org,
	jarkko@kernel.org, luto@kernel.org, dave.hansen@intel.com,
	haitao.huang@intel.com, pbonzini@redhat.com, tglx@linutronix.de,
	mingo@redhat.com, hpa@zytor.com
Subject: Re: [RFC PATCH v2 01/26] x86/cpufeatures: Add SGX1 and SGX2 sub-features
Date: Wed, 20 Jan 2021 11:54:59 +1300	[thread overview]
Message-ID: <973a42cd008fb28a3b76aeefc3231091e24a0724.camel@intel.com> (raw)
In-Reply-To: <YAce4r4QhGzJqd4y@google.com>

On Tue, 2021-01-19 at 10:03 -0800, Sean Christopherson wrote:
> On Tue, Jan 19, 2021, Borislav Petkov wrote:
> > On Mon, Jan 18, 2021 at 04:26:49PM +1300, Kai Huang wrote:
> > > diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
> > > index 3b1b01f2b248..7937a315f8cf 100644
> > > --- a/arch/x86/kernel/cpu/feat_ctl.c
> > > +++ b/arch/x86/kernel/cpu/feat_ctl.c
> > > @@ -96,7 +96,6 @@ static void init_vmx_capabilities(struct cpuinfo_x86 *c)
> > >  static void clear_sgx_caps(void)
> > >  {
> > >  	setup_clear_cpu_cap(X86_FEATURE_SGX);
> > > -	setup_clear_cpu_cap(X86_FEATURE_SGX_LC);
> > 
> > Why is that line being removed here?
> > 
> > Shouldn't this add SGX1 and SGX2 here instead as this function is
> > supposed to, well, *clear* sgx caps on feat_ctl setup failures or
> > "nosgx" cmdline?
> 
> Doesn't adding making the SGX sub-features depend on X86_FEATURE_SGX have the
> same net effect?  Or am I misreading do_clear_cpu_cap()?

On my testing machine with SGX, SGX_LC, and SGX1. I just double tested that clearing
X86_FEATURE_SGX also clears SGX1 and SGX_LC bits.

> 
> Though if we use the cpuid_deps table, I'd vote to get rid of clear_sgx_caps()
> and call setup_clear_cpu_cap(X86_FEATURE_SGX) directly. 
> 

Yes I can do that.

>  And probably change the
> existing SGX_LC behavior and drop clear_sgx_caps() in a separate patch instead
> of squeezing it into this one.

To double confirm, you want:

1) This patch to introduce SGX1, SGX2, and also put SGX1 and SGX2 in to CPUID
dependency table; 
2) A separate patch to put SGX_LC to CPUID dependency table too, and also git rid of
clear_sgx_caps()

Correct?

Btw, in your original patch, both SGX1 and SGX2 depends on SGX, but I changed to make
SGX2 depend on SGX1. However I still make SGX_LC depend on SGX, but not SGX1. Does
this make sense to you?