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

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Date:   Mon, 15 Mar 2021 16:13:17 +1300
From:   Kai Huang <kai.huang@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Sean Christopherson <seanjc@...gle.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 Sun, 14 Mar 2021 17:27:18 +0200 Jarkko Sakkinen wrote:
> On Sun, Mar 14, 2021 at 05:25:26PM +0200, Jarkko Sakkinen wrote:
> > On Sat, Mar 13, 2021 at 09:07:36PM +0200, Jarkko Sakkinen wrote:
> > > 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?
> >  
> > Apologies coming with these ideas at this point, but here is what this
> > led me.
> > 
> > I think that the all this complexity comes from a bad code structure.
> > 
> > So, what is essentially happening here:
> > 
> > - We essentially want to make EPC always work.
> > - Driver optionally.
> > 
> > So what this sums to is something like:
> > 
> >         ret = sgx_epc_init();
> >         if (ret) {
> >                 pr_err("EPC initialization failed.\n");
> >                 return ret;
> >         }
> > 
> >         ret = sgx_drv_init();
> >         if (ret)
> >                 pr_info("Driver could not be initialized.\n");
> > 
> >         /* continue */
> > 
> > I.e. I think there should be a single EPC init, which does both EPC
> > bootstrapping and vepc, and driver initialization comes after that.
> 
> In other words, from SGX point of view, the thing that KVM needs is
> to cut out EPC and driver part into different islands. How this is now
> implemented in the current patch set is half-way there but not yet what
> it should be.

Well conceptually, SGX virtualization and SGX driver are two independently
functionalities can be enabled separately, although they both requires some
come functionalities, such as /dev/sgx_provision, which we have moved to
sgx/main.c exactly for this purpose. THerefore, conceptually, it is bad to make
assumption that, if SGX virtualization initialization succeeded, SGX driver
must succeed -- we can potentially add more staff in SGX virtualization in the
future..

If the name sgx_vepc_init() confuses you, I can rename it to sgx_virt_init().

Hi Sean,

Please let us know if you have comments.