linux-kernel - Re: [PATCH Part1 v5 34/38] x86/sev: Add snp_msg

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Message-ID: <YTC1ANx81eQeGN4o@zn.tnic>
Date:   Thu, 2 Sep 2021 13:26:56 +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,
        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>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>, tony.luck@...el.com,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH Part1 v5 34/38] x86/sev: Add snp_msg_seqno() helper

On Mon, Aug 30, 2021 at 10:07:39AM -0500, Brijesh Singh wrote:
> The SNP firmware spec says that counter must begin with the 1.

So put that in the comment and explain what 0 is: magic or invalid or
whatnot and why is that so and that it is spec-ed this way, etc.

Just having it there without a reasoning makes one wonder whether that's
some arbitrary limitation or so.

> During the GHCB writing the seqno use to be 32-bit value and hence the GHCB
> spec choose the 32-bit value but recently the SNP firmware changed it from
> the 32 to 64. So, now we are left with the option of limiting the sequence
> number to 32-bit. If we go beyond 32-bit then all we can do is fail the
> call. If we pass the value of zero then FW will fail the call.

That sounds weird again. So make it 64-bit like the FW and fix the spec.

> I just choose the smaller name but I have no issues matching with the spec.
> Also those keys does not have anything to do with the VMPL level. The
> secrets page provides 4 different keys and they are referred as vmpck0..3
> and each of them have a sequence numbers associated with it.
> 
> In GHCB v3 we probably need to rework the structure name.

You can point to the spec section so that readers can find the struct
layout there.

-- 
Regards/Gruss,
    Boris.

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