linux-kernel - Re: [PATCH v2] x86/sev: Add SEV-SNP guest feature negotiation support

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Date:   Mon, 5 Dec 2022 16:46:48 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Nikunj A Dadhania <nikunj@....com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, kvm@...r.kernel.org, mingo@...hat.com,
        tglx@...utronix.de, dave.hansen@...ux.intel.com, seanjc@...gle.com,
        pbonzini@...hat.com, michael.roth@....com, stable@...nel.org
Subject: Re: [PATCH v2] x86/sev: Add SEV-SNP guest feature negotiation support

On Mon, Dec 05, 2022 at 09:23:17AM -0600, Tom Lendacky wrote:
> This makes it sound like these features are required to run SNP, which
> they're not. It's that we can't run SNP with these features without support
> in the guest. So while the patch name is long, it is accurate.

Maybe, but it is a mouthful this way. And unreadable. And there's plenty
of comments explaining what it is. And it is used in one place only.

> Maybe SNP_FEATURES_NEED_IMPLEMENTATION if you want to shorten it a little?

"need implementation" where? Host? Guest?

I.e., we're relying on comments to explain what the name is, one way or
the other.

How about a short and sweet:

		if (sev_status & SNP_FEATURES_IMPL_REQ & ~SNP_FEATURES_PRESENT)

along with the explanation in a comment above it. Comment which is a
must regardless.

Hmm.

-- 
Regards/Gruss,
    Boris.

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