linux-kernel - Re: [PATCH Part1 RFC v4 22/36] x86/sev: move MSR-based VMGEXITs for CPUID to helper

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Date:   Thu, 19 Aug 2021 18:46:48 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Michael Roth <michael.roth@....com>
Cc:     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,
        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>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        brijesh.ksingh@...il.com
Subject: Re: [PATCH Part1 RFC v4 22/36] x86/sev: move MSR-based VMGEXITs for
 CPUID to helper

On Thu, Aug 19, 2021 at 10:37:41AM -0500, Michael Roth wrote:
> That makes sense, but I think it helps in making sense of the security
> aspects of the code to know that sev_cpuid() would be fetching cpuid
> information from the hypervisor.

Why is it important for the callers to know where do we fetch the CPUID
info from?

> "msr_proto" is meant to be an indicator that it will be using the GHCB
> MSR protocol to do it, but maybe just "_hyp" is enough to get the idea
> across? I use the convention elsewhere in the series as well.
>
> So sev_cpuid_hyp() maybe?

sev_cpuid_hv() pls. We abbreviate the hypervisor as HV usually.

> In "enable SEV-SNP-validated CPUID in #VC handler", it does:
>
>   sev_snp_cpuid() -> sev_snp_cpuid_hyp(),
>
> which will call this with NULL e{a,b,c,d}x arguments in some cases. There
> are enough call-sites in sev_snp_cpuid() that it seemed worthwhile to
> add the guards so we wouldn't need to declare dummy variables for arguments.

Yah, saw that in the later patches.

Thx.

-- 
Regards/Gruss,
    Boris.

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