linux-kernel - Re: [PATCH Part1 RFC v3 11/22] x86/sev: Add helper for validating pages in early enc attribute changes

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Message-ID: <YMnoeRcuMfAqX5Vf@zn.tnic>
Date:   Wed, 16 Jun 2021 14:03:05 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>, tony.luck@...el.com,
        npmccallum@...hat.com
Subject: Re: [PATCH Part1 RFC v3 11/22] x86/sev: Add helper for validating
 pages in early enc attribute changes

On Wed, Jun 16, 2021 at 06:00:09AM -0500, Brijesh Singh wrote:
> I am trying to be consistent with previous VMGEXIT implementations. If
> the command itself failed then use the command specific error code to
> tell hypervisor why we terminated but if the hypervisor violated the
> GHCB specification then use the "general request termination".

I feel like we're running in circles here: I ask about debuggability
and telling the user what exactly failed and you're giving me some
explanation about what the error codes mean. I can see what they mean.

So let me try again:

Imagine you're a guest owner and you haven't written the SNP code and
you don't know how it works.

You start a guest in the public cloud and it fails because the
hypervisor violates the GHCB protocol and all that guest prints before
it dies is

"general request termination"

How are you - the guest owner - going to find out what exactly happened?

Call support?

-- 
Regards/Gruss,
    Boris.

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