linux-kernel - Re: [PATCH Part1 v5 32/38] x86/sev: enable SEV-SNP-validated CPUID in #VC handlers

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Message-ID: <20210901011658.s4hgmvbptgseqcm3@amd.com>
Date:   Tue, 31 Aug 2021 20:16:58 -0500
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>,
        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>,
        "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 32/38] x86/sev: enable SEV-SNP-validated CPUID
 in #VC handlers

On Tue, Aug 31, 2021 at 06:22:44PM +0200, Borislav Petkov wrote:
> On Fri, Aug 27, 2021 at 01:32:40PM -0500, Michael Roth wrote:
> > If the memory is allocated in boot/compressed/mem_encrypt.S, wouldn't
> > kernel proper still need to create a static buffer for its copy?
> 
> Just like the other variables like sme_me_mask etc that file allocates
> at the bottom. Or do you have a better idea?

What did you think of the suggestion of defining it in sev-shared.c
as a static buffer/struct as __ro_after_init? It would be nice to
declare/reserve the memory in one place. Another benefit is it doesn't
need to be exported, and could just be local with all the other
snp_cpuid* helpers that access it in sev-shared.c

> 
> > Would that be a reasonable approach for v6?
> 
> I don't like the ifdeffery one bit, TBH. I guess you should split it
> and have a boot/compressed page and a kernel proper one and keep 'em
> separate. That should make everything nice and clean at the cost of 2*4K
> which is nothing nowadays.

I think I can address the ifdeffery by splitting the boot/proper routines
into separate self-contained routines (and maybe move them out into
boot/compressed/sev.c and kernel/sev.c, respectively), then having them
just initialize the table pointer and create the copy using a common setter
function, e.g.

  snp_cpuid_table_create(cc_blob, fixup_offset)

and for boot/compressed.c fixup_offset would just be passed in as 0.

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