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 18:13:53 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
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 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.

>    For KVM getting init'd with SGX, on the other hand, we have good
>    practical reasons.
> 2. We can get something practically useful with simpler and more verbose
>    code, i.e. better logging.
> 
> /Jarkko