linux-kernel - Re: [PATCH v2 07/25] x86/sgx: Initialize virtual EPC driver even when SGX driver is disabled

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Date:   Sat, 13 Mar 2021 21:07:36 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Kai Huang <kai.huang@...el.com>, kvm@...r.kernel.org,
        linux-sgx@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, luto@...nel.org,
        dave.hansen@...el.com, rick.p.edgecombe@...el.com,
        haitao.huang@...el.com, pbonzini@...hat.com, bp@...en8.de,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com
Subject: Re: [PATCH v2 07/25] x86/sgx: Initialize virtual EPC driver even
 when SGX driver is disabled

On Sat, Mar 13, 2021 at 09:05:36PM +0200, Jarkko Sakkinen wrote:
> On Fri, Mar 12, 2021 at 01:44:58PM -0800, Sean Christopherson wrote:
> > On Tue, Mar 09, 2021, Kai Huang wrote:
> > > Modify sgx_init() to always try to initialize the virtual EPC driver,
> > > even if the SGX driver is disabled.  The SGX driver might be disabled
> > > if SGX Launch Control is in locked mode, or not supported in the
> > > hardware at all.  This allows (non-Linux) guests that support non-LC
> > > configurations to use SGX.
> > > 
> > > Acked-by: Dave Hansen <dave.hansen@...el.com>
> > > Signed-off-by: Kai Huang <kai.huang@...el.com>
> > > ---
> > >  arch/x86/kernel/cpu/sgx/main.c | 10 +++++++++-
> > >  1 file changed, 9 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> > > index 44fe91a5bfb3..8c922e68274d 100644
> > > --- a/arch/x86/kernel/cpu/sgx/main.c
> > > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > > @@ -712,7 +712,15 @@ static int __init sgx_init(void)
> > >  		goto err_page_cache;
> > >  	}
> > >  
> > > -	ret = sgx_drv_init();
> > > +	/*
> > > +	 * Always try to initialize the native *and* KVM drivers.
> > > +	 * The KVM driver is less picky than the native one and
> > > +	 * can function if the native one is not supported on the
> > > +	 * current system or fails to initialize.
> > > +	 *
> > > +	 * Error out only if both fail to initialize.
> > > +	 */
> > > +	ret = !!sgx_drv_init() & !!sgx_vepc_init();
> > 
> > I love this code.
> > 
> > Reviewed-by: Sean Christopherson <seanjc@...gle.com>
> 
> I'm still wondering why this code let's go through when sgx_drv_init()
> succeeds and sgx_vepc_init() fails.
> 
> The inline comment explains only the mirrored case (which does make
> sense).

I.e. if sgx_drv_init() succeeds, I'd expect that sgx_vepc_init() must
succeed. Why expect legitly anything else?

/Jarkko