linux-kernel - Re: [PATCH v11 39/45] x86/sev: Use firmware-validated CPUID for SEV-SNP guests

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Date:   Thu, 3 Mar 2022 18:31:57 -0600
From:   Michael Roth <michael.roth@....com>
To:     Borislav Petkov <bp@...en8.de>
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>,
        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>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        <brijesh.ksingh@...il.com>, <tony.luck@...el.com>,
        <marcorr@...gle.com>, <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v11 39/45] x86/sev: Use firmware-validated CPUID for
 SEV-SNP guests

On Thu, Mar 03, 2022 at 12:51:20PM +0100, Borislav Petkov wrote:
> On Thu, Feb 24, 2022 at 10:56:19AM -0600, Brijesh Singh wrote:
> > Also add an "sev_debug" kernel command-line parameter that will be used
> > (initially) to dump the CPUID table for debugging/analysis.
> 
> No, not "sev_debug" - "sev=debug".
> 
> I'm pretty sure there will be need for other SEV-specific cmdline
> options so this thing should be a set, i.e.,
> 	"sev=(option1,option2?,option3?,...)"
> 
> etc.
> 
> See mcheck_enable() and the comment above it for an example.

If I do it the mce_check() way it ends up looking something like the
below, is that what you add in mind?

In that case it seems to expect "mce=option1 mce=option2" etc. I could
open-code a parser to handle multiple options like sev=option1,option2
etc., but wanted to check with you first.

Also, should I go ahead and introduce struct sev_options now, or
just use a regular bool until more options are added later?

Thanks!

struct sev_options {
       bool debug;
};

static struct sev_options sev_cmdline_opts;

...

static int __init process_sev_options(char *str)
{
       if ((*str) == '=')
               str++;

       if (!strcmp(str, "debug")) {
               sev_cmdline_opts.debug = true;
       } else {
               pr_info("SEV command-line option '%s' was not ecognized\n", str);
               return 1;
       }

       return 0;
}
__setup("sev", process_sev_options);

static int __init report_cpuid_table(void)
{
    ...
    if (sev_cmdline_opts.debug)
        dump_cpuid_table();
}
arch_initcall(report_cpuid_table)

> 
> -- 
> Regards/Gruss,
>     Boris.
> 
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