linux-kernel - Re: [PATCH 06/25] x86/cpu/intel: Allow SGX virtualization without Launch Control support

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Date:   Mon, 8 Mar 2021 13:19:41 +1300
From:   Kai Huang <kai.huang@...el.com>
To:     Kai Huang <kai.huang@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>, <kvm@...r.kernel.org>,
        <x86@...nel.org>, <linux-sgx@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <seanjc@...gle.com>,
        <jarkko@...nel.org>, <luto@...nel.org>, <dave.hansen@...el.com>,
        <rick.p.edgecombe@...el.com>, <haitao.huang@...el.com>,
        <pbonzini@...hat.com>, <tglx@...utronix.de>, <mingo@...hat.com>,
        <hpa@...or.com>, <jethro@...tanix.com>, <b.thiel@...teo.de>
Subject: Re: [PATCH 06/25] x86/cpu/intel: Allow SGX virtualization without
 Launch Control support

On Mon, 8 Mar 2021 12:50:26 +1300 Kai Huang wrote:
> On Fri, 5 Mar 2021 18:29:57 +0100 Borislav Petkov wrote:
> > On Mon, Mar 01, 2021 at 10:45:02PM +1300, Kai Huang wrote:
> > > From: Sean Christopherson <sean.j.christopherson@...el.com>
> > > 
> > > The kernel will currently disable all SGX support if the hardware does
> > > not support launch control.  Make it more permissive to allow SGX
> > > virtualization on systems without Launch Control support.  This will
> > > allow KVM to expose SGX to guests that have less-strict requirements on
> > > the availability of flexible launch control.
> > > 
> > > Improve error message to distinguish between three cases.  There are two
> > > cases where SGX support is completely disabled:
> > > 1) SGX has been disabled completely by the BIOS
> > > 2) SGX LC is locked by the BIOS.  Bare-metal support is disabled because
> > >    of LC unavailability.  SGX virtualization is unavailable (because of
> > >    Kconfig).
> > > One where it is partially available:
> > > 3) SGX LC is locked by the BIOS.  Bare-metal support is disabled because
> > >    of LC unavailability.  SGX virtualization is supported.
> > > 
> > > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > > Co-developed-by: Kai Huang <kai.huang@...el.com>
> > > Acked-by: Dave Hansen <dave.hansen@...el.com>
> > > Signed-off-by: Kai Huang <kai.huang@...el.com>
> > > ---
> > >  arch/x86/kernel/cpu/feat_ctl.c | 57 ++++++++++++++++++++++++++--------
> > >  1 file changed, 44 insertions(+), 13 deletions(-)
> > > 
> > > diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
> > > index 27533a6e04fa..96c370284913 100644
> > > --- a/arch/x86/kernel/cpu/feat_ctl.c
> > > +++ b/arch/x86/kernel/cpu/feat_ctl.c
> > > @@ -105,7 +105,8 @@ early_param("nosgx", nosgx);
> > >  void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
> > >  {
> > >  	bool tboot = tboot_enabled();
> > > -	bool enable_sgx;
> > > +	bool enable_sgx_any, enable_sgx_kvm, enable_sgx_driver;
> > > +	bool enable_vmx;
> > >  	u64 msr;
> > 
> > The preferred ordering of variable declarations at the beginning of a
> > function is reverse fir tree order::
> > 
> > 	struct long_struct_name *descriptive_name;
> > 	unsigned long foo, bar;
> > 	unsigned int tmp;
> > 	int ret;
> > 
> 
> Will do.
> 
> Since as you suggested, enable_sgx_any will be removed, and initializing
> enable_sgx_driver/kvm will be moved into the if () statement, I think we should
> explicitly initialize them here. How about below?
> 
> 	bool enable_sgx_kvm = enable_sgx_driver = false;

Sorry my bad, should be:

	bool enable_sgx_kvm = false, enable_sgx_driver = false;

> 	bool tboot = tboot_enabled();
> 	bool enable_vmx;
> 	...
> 
> > 
> > >  	if (rdmsrl_safe(MSR_IA32_FEAT_CTL, &msr)) {
> > > @@ -114,13 +115,21 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
> > >  		return;
> > >  	}
> > >  
> > > +	enable_vmx = cpu_has(c, X86_FEATURE_VMX) &&
> > > +		     IS_ENABLED(CONFIG_KVM_INTEL);
> > > +
> > >  	/*
> > > -	 * Enable SGX if and only if the kernel supports SGX and Launch Control
> > > -	 * is supported, i.e. disable SGX if the LE hash MSRs can't be written.
> > > +	 * Separate out SGX driver enabling from KVM.  This allows KVM
> > > +	 * guests to use SGX even if the kernel SGX driver refuses to
> > > +	 * use it.  This happens if flexible Faunch Control is not
> > > +	 * available.
> > >  	 */
> > > -	enable_sgx = cpu_has(c, X86_FEATURE_SGX) &&
> > > -		     cpu_has(c, X86_FEATURE_SGX_LC) &&
> > > -		     IS_ENABLED(CONFIG_X86_SGX);
> > > +	enable_sgx_any = cpu_has(c, X86_FEATURE_SGX) &&
> > > +			 IS_ENABLED(CONFIG_X86_SGX);
> > > +	enable_sgx_driver = enable_sgx_any &&
> > > +			    cpu_has(c, X86_FEATURE_SGX_LC);
> > > +	enable_sgx_kvm = enable_sgx_any && enable_vmx &&
> > > +			  IS_ENABLED(CONFIG_X86_SGX_KVM);
> > 
> > That enable_sgx_any use looks weird. You can get rid of it:
> > 
> > 	if (cpu_has(c, X86_FEATURE_SGX) && IS_ENABLED(CONFIG_X86_SGX)) {
> > 		enable_sgx_driver = cpu_has(c, X86_FEATURE_SGX_LC);
> > 		enable_sgx_kvm    = enable_vmx && IS_ENABLED(CONFIG_X86_SGX_KVM);
> > 	}
> > 
> > and yap, let longer lines stick out.
> 
> Thanks. Will do.
> 
> > 
> > Thx.
> > 
> > -- 
> > Regards/Gruss,
> >     Boris.
> > 
> > https://people.kernel.org/tglx/notes-about-netiquette