linux-kernel - Re: [PATCH v3 07/25] x86/sgx: Initialize virtual EPC driver even when SGX driver is disabled

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Date:   Fri, 2 Apr 2021 15:42:51 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Kai Huang <kai.huang@...el.com>, kvm@...r.kernel.org,
        linux-sgx@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, 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
Subject: Re: [PATCH v3 07/25] x86/sgx: Initialize virtual EPC driver even
 when SGX driver is disabled

On Fri, Apr 02, 2021, Borislav Petkov wrote:
> On Fri, Mar 19, 2021 at 08:23:02PM +1300, 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>
> > Reviewed-by: Sean Christopherson <seanjc@...gle.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 6a734f484aa7..b73114150ff8 100644
> > --- a/arch/x86/kernel/cpu/sgx/main.c
> > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > @@ -743,7 +743,15 @@ 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();
> 
> This is a silly way of writing:
> 
>         if (sgx_drv_init() && sgx_vepc_init())
>                 goto err_kthread;
> 
> methinks.

Nope!  That's wrong, as sgx_epc_init() will not be called if sgx_drv_init()
succeeds.  And writing it as "if (sgx_drv_init() || sgx_vepc_init())" is also
wrong since that would kill SGX when one of the drivers is alive and well.