Date:   Wed, 15 Dec 2021 19:33:47 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Venu Busireddy <venu.busireddy@oracle.com>
Cc:     Michael Roth <michael.roth@amd.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Brijesh Singh <brijesh.singh@amd.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andi Kleen <ak@linux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH v8 01/40] x86/compressed/64: detect/setup SEV/SME
 features earlier in boot
Message-ID: <Ybo1C6kpcPJBzMGq@zn.tnic>
References: <20211210154332.11526-1-brijesh.singh@amd.com>
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On Wed, Dec 15, 2021 at 12:17:44PM -0600, Venu Busireddy wrote:
> Boris & Tom, which implementation would you prefer?

I'd like to see how that sme_sev_parse_cpuid() would look like. And that
function should be called sev_parse_cpuid(), btw.

Because if that function turns out to be a subset of your suggestion,
functionality-wise, then we should save us the churn and simply do one
generic helper.

Btw 2, that helper should be in arch/x86/kernel/sev-shared.c so that it
gets shared by both kernel stages instead having an inline function in
some random header.

Btw 3, I'm not crazy about the feature testing with the @features param
either. Maybe that function should return the eYx register directly,
like the cpuid_eYx() variants in the kernel do, where Y in { a, b, c, d
}.

The caller can than do its own testing:

	eax = sev_parse_cpuid(RET_EAX, ...)
	if (eax > 0) {
		if (eax & BIT(1))
			...

Something along those lines, for example.

But I'd have to see a concrete diff from Michael to get a better idea
how that CPUID parsing from the CPUID page is going to look like.

Thx.

-- 
Regards/Gruss,
    Boris.

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