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

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Date:   Tue, 16 Mar 2021 14:46:05 +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 Mon, Mar 15, 2021 at 06:13:53PM -0700, Sean Christopherson wrote:
> On Tue, Mar 16, 2021, Jarkko Sakkinen wrote:
> > On Tue, Mar 16, 2021 at 01:05:05AM +0200, Jarkko Sakkinen wrote:
> > > The way I've understood it is that given that KVM can support SGX
> > > without FLC, vEPC should be available even if driver cannot be
> > > enabled.
> > > 
> > > This is also exactly what the short summary states.
> > > 
> > > "Initialize virtual EPC driver even when SGX driver is disabled"
> > > 
> > > It *does not* state:
> > > 
> > > "Initialize SGX driver even when vEPC driver is disabled"
> > > 
> > > Also, this is how I interpret the inline comment.
> > > 
> > > All this considered, the other direction is undocumented functionality.
> > 
> > Also:
> > 
> > 1. There is *zero* good practical reasons to support the "2nd direction".
> 
> Uh, yes there is.  CONFIG_KVM_INTEL=n and X86_FEATURE_VMX=n, either of which
> will cause vEPC initialization to fail.  The former is obvious, the latter is
> possible via BIOS configuration.

Hmm... So you make the checks as if ret != -ENODEV? That's the sane way to
deal with that situation IMHO.

/Jarkko