linux-kernel - Re: [PATCH v8 29/40] x86/compressed/64: add support for SEV-SNP CPUID table in #VC handlers

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Message-ID: <YebIiN6Ftq2aPtyF@zn.tnic>
Date:   Tue, 18 Jan 2022 15:02:48 +0100
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,
        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@...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 29/40] x86/compressed/64: add support for SEV-SNP
 CPUID table in #VC handlers

On Mon, Jan 17, 2022 at 10:35:21PM -0600, Michael Roth wrote:
> Unfortunately, in sev_enable(), between the point where snp_init() is
> called, and sev_status is actually set, there are a number of cpuid
> intructions which will make use of do_vc_no_ghcb() prior to sev_status
> being set (and it needs to happen in that order to set sev_status
> appropriately). After that point, snp_cpuid_active() would no longer be
> necessary, but during that span some indicator is needed in case this
> is just an SEV-ES guest trigger cpuid #VCs.

You mean testing what snp_cpuid_info_create() set up is not enough?

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 7bc7e297f88c..17cfe804bad3 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -523,7 +523,9 @@ static int snp_cpuid_postprocess(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
 static int snp_cpuid(u32 func, u32 subfunc, u32 *eax, u32 *ebx, u32 *ecx,
 		     u32 *edx)
 {
-	if (!snp_cpuid_active())
+	const struct snp_cpuid_info *c = snp_cpuid_info_get_ptr();
+
+	if (!c->count)
 		return -EOPNOTSUPP;
 
 	if (!snp_cpuid_find_validated_func(func, subfunc, eax, ebx, ecx, edx)) {

---

Btw, all those

        /* SEV-SNP CPUID table should be set up now. */
        if (!snp_cpuid_active())
                sev_es_terminate(1, GHCB_TERM_CPUID);

after snp_cpuid_info_create() has returned are useless either. If that
function returns, you know you're good to go wrt SNP.

Thx.

-- 
Regards/Gruss,
    Boris.

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