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Date:   Tue, 18 Jan 2022 15:02:48 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Michael Roth <michael.roth@amd.com>
Cc:     Brijesh Singh <brijesh.singh@amd.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
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        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
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        Jim Mattson <jmattson@google.com>,
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Subject: Re: [PATCH v8 29/40] x86/compressed/64: add support for SEV-SNP
 CPUID table in #VC handlers
Message-ID: <YebIiN6Ftq2aPtyF@zn.tnic>
References: <20211210154332.11526-1-brijesh.singh@amd.com>
 <20211210154332.11526-30-brijesh.singh@amd.com>
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 <20220113163913.phpu4klrmrnedgic@amd.com>
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 <20220118043521.exgma53qrzrbalpd@amd.com>
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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