linux-kernel - Re: [PATCH 02/25] x86/cpufeatures: Add SGX1 and SGX2 sub-features

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Date:   Mon, 1 Mar 2021 11:53:46 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Kai Huang <kai.huang@...el.com>
Cc:     kvm@...r.kernel.org, x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, seanjc@...gle.com, 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 02/25] x86/cpufeatures: Add SGX1 and SGX2 sub-features

On Mon, Mar 01, 2021 at 11:40:02PM +1300, Kai Huang wrote:
> SGX2 means "Enclave Dynamic Memory Management", which supports dynamically
> adding/removing EPC pages, plus changing page permission, after enclave is
> initialized. So it allows enclave author to write enclave in more flexible way, and
> also utilize EPC resource more efficiently.

So how is the enclave author going to use "sgx2" in /proc/cpuinfo? Query
it to know whether it can start adding/removing EPC pages or is this
going to be used by scripts?

> Yes I can add "why" into commit message, but isn't the comment after X86_FEATURE_SGX2
> enough? I think people who are interested in SGX will know what SGX2 is and why SGX2
> is useful.

The point is, the commit message should say how this flag in
/proc/cpuinfo is going to be used - not what people interested in sgx
might and might not know.

/proc/cpuinfo is user-visible ABI - you can't add stuff to it just because.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette