linux-kernel - Re: [PATCH v8 35/40] x86/sev: use firmware-validated CPUID for SEV-SNP guests

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Date:   Wed, 26 Jan 2022 19:35:04 +0100
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>,
        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>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v8 35/40] x86/sev: use firmware-validated CPUID for
 SEV-SNP guests

On Fri, Dec 10, 2021 at 09:43:27AM -0600, Brijesh Singh wrote:
> From: Michael Roth <michael.roth@....com>
> 
> SEV-SNP guests will be provided the location of special 'secrets' and
> 'CPUID' pages via the Confidential Computing blob. This blob is
> provided to the run-time kernel either through bootparams field that
						^
						a


> was initialized by the boot/compressed kernel, or via a setup_data
> structure as defined by the Linux Boot Protocol.
> 
> Locate the Confidential Computing from these sources and, if found,
				   ^
				   blob

> use the provided CPUID page/table address to create a copy that the
> run-time kernel will use when servicing cpuid instructions via a #VC
					  ^^^^^

Please capitalize all instruction mnemonics in text.

> +/*
> + * It is useful from an auditing/testing perspective to provide an easy way
> + * for the guest owner to know that the CPUID table has been initialized as
> + * expected, but that initialization happens too early in boot to print any
> + * sort of indicator, and there's not really any other good place to do it. So
> + * do it here, and while at it, go ahead and re-verify that nothing strange has
> + * happened between early boot and now.
> + */
> +static int __init snp_cpuid_check_status(void)

That function's redundant now, I believe, since we terminate the guest
if there's something wrong with the CPUID page.

-- 
Regards/Gruss,
    Boris.

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