linux-kernel - Re: [PATCH v8 01/40] x86/compressed/64: detect/setup SEV/SME features earlier in boot

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Date:   Wed, 15 Dec 2021 12:17:44 -0600
From:   Venu Busireddy <venu.busireddy@...cle.com>
To:     Michael Roth <michael.roth@....com>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...en8.de>,
        Brijesh Singh <brijesh.singh@....com>, 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>,
        "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>,
        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>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v8 01/40] x86/compressed/64: detect/setup SEV/SME
 features earlier in boot

On 2021-12-15 11:49:34 -0600, Michael Roth wrote:
> 
> I think in the greater context of consolidating all the SME/SEV setup
> and re-using code, this helper stands a high chance of eventually becoming
> something more along the lines of sme_sev_parse_cpuid(), since otherwise
> we'd end up re-introducing multiple helpers to parse the same 0x8000001F
> fields if we ever need to process any of the other fields advertised in
> there. Given that, it makes sense to reserve the return value as an
> indication that either SEV or SME are enabled, and then have a
> pass-by-pointer parameters list to collect the individual feature
> bits/encryption mask for cases where SEV/SME are enabled, which are only
> treated as valid if sme_sev_parse_cpuid() returns 0.
> 
> So Venu's original approach of passing the encryption mask by pointer
> seems a little closer toward that end, but I also agree Tom's approach
> is cleaner for the current code base, so I'm fine either way, just
> figured I'd mention this.
> 
> I think needing to pass in the SME/SEV CPUID bits to tell the helper when
> to parse encryption bit and when not to is a little bit awkward though.
> If there's some agreement that this will ultimately serve the purpose of
> handling all (or most) of SME/SEV-related CPUID parsing, then the caller
> shouldn't really need to be aware of any individual bit positions.
> Maybe a bool could handle that instead, e.g.:
> 
>   int get_me_bit(bool sev_only, ...)
> 
>   or
> 
>   int sme_sev_parse_cpuid(bool sev_only, ...)
> 
> where for boot/compressed sev_only=true, for kernel proper sev_only=false.

I can implement it this way too. But I am wondering if having a
boolean argument limits us from handling any future additions to the
bit positions.

Boris & Tom, which implementation would you prefer?

Venu