Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Received-SPF: Pass (protection.outlook.com: domain of amd.com designates
 165.204.84.17 as permitted sender) receiver=protection.outlook.com;
 client-ip=165.204.84.17; helo=SATLEXMB04.amd.com;
Date:   Tue, 18 Jan 2022 08:23:45 -0600
From:   Michael Roth <michael.roth@amd.com>
To:     Borislav Petkov <bp@alien8.de>
CC:     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>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "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 29/40] x86/compressed/64: add support for SEV-SNP
 CPUID table in #VC handlers
Message-ID: <20220118142345.65wuub2p3alavhpb@amd.com>
References: <20211210154332.11526-1-brijesh.singh@amd.com>
 <20211210154332.11526-30-brijesh.singh@amd.com>
 <YeAmFePcPjvMoWCP@zn.tnic>
 <20220113163913.phpu4klrmrnedgic@amd.com>
 <YeGhKll2fTcTr2wS@zn.tnic>
 <20220118043521.exgma53qrzrbalpd@amd.com>
 <YebIiN6Ftq2aPtyF@zn.tnic>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <YebIiN6Ftq2aPtyF@zn.tnic>
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jan 2022 14:24:05.0932
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 15d5387d-b403-4f58-928d-08d9da8e2e95
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com]
X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT021.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4093
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Jan 18, 2022 at 03:02:48PM +0100, Borislav Petkov wrote:
> 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)) {

snp_cpuid_info_get_ptr() will always return non-NULL, since it's a
pointer to the local copy of the cpuid page. But I can probably re-work
it slightly that so snp_cpuid_info_get_ptr() does the same check that
snp_cpuid_active() does, and have it return NULL if the copy hasn't been
initialized, if that seems preferable to the separate snp_cpuid_active()
function.

> 
> ---
> 
> 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.

It seemed like a good thing to assert in case something slipped in later
that tried to use snp_cpuid() without the table being initialized, but
if I implement things the way you suggested above,
snp_cpuid_info_get_ptr() will return NULL in that case, so we get that
assurance for free. That does sound cleaner.

> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpeople.kernel.org%2Ftglx%2Fnotes-about-netiquette&amp;data=04%7C01%7Cmichael.roth%40amd.com%7Cb8be348c4db84954006708d9da8b3820%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637781113782595576%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=HszNjYntQNNI827LNK4H8Tpx0vhpICo7y3FCzIvhNtc%3D&amp;reserved=0