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David Alan Gilbert" , , , Subject: Re: [PATCH v8 29/40] x86/compressed/64: add support for SEV-SNP CPUID table in #VC handlers Message-ID: <20220118143730.wenhm2bbityq7wwy@amd.com> References: <20211210154332.11526-1-brijesh.singh@amd.com> <20211210154332.11526-30-brijesh.singh@amd.com> <20220113163913.phpu4klrmrnedgic@amd.com> <20220118043521.exgma53qrzrbalpd@amd.com> <20220118142345.65wuub2p3alavhpb@amd.com> <20220118143238.lu22npcktxuvadwk@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20220118143238.lu22npcktxuvadwk@amd.com> X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB03.amd.com (10.181.40.144) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: e4dbac7d-ecca-43bb-0665-08d9da9019da X-MS-TrafficTypeDiagnostic: CO6PR12MB5459:EE_ X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8882; X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB04.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(4636009)(46966006)(40470700002)(36840700001)(1076003)(44832011)(2616005)(186003)(36860700001)(426003)(316002)(70206006)(70586007)(8676002)(54906003)(16526019)(336012)(47076005)(8936002)(40460700001)(508600001)(82310400004)(86362001)(6666004)(81166007)(4326008)(5660300002)(356005)(83380400001)(7406005)(36756003)(26005)(7416002)(2906002)(6916009)(36900700001);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jan 2022 14:37:49.2719 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: e4dbac7d-ecca-43bb-0665-08d9da9019da 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: DM6NAM11FT024.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CO6PR12MB5459 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 18, 2022 at 08:32:38AM -0600, Michael Roth wrote: > On Tue, Jan 18, 2022 at 08:23:45AM -0600, Michael Roth wrote: > > 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 > > Doh, misread your patch. Yes I think checking the count would also work, > since a valid table should be non-zero. Actually, no, because doing that would provide hypervisor a means to effectively disable CPUID page for an SNP guest by provided a table with count == 0, which needs to be guarded against. But can still implement something similar by having snp_cpuid_info_get_ptr() return NULL if local copy of cpuid page hasn't been initialized.