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smtp.mailfrom=brijesh.singh@amd.com; Received: from [10.236.136.62] (165.204.77.1) by BYAPR12MB2680.namprd12.prod.outlook.com (2603:10b6:a03:69::29) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.1080.13; Fri, 24 Aug 2018 15:41:37 +0000 Cc: brijesh.singh@amd.com, Borislav Petkov , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "Lendacky, Thomas" , Thomas Gleixner Subject: Re: SEV guest regression in 4.18 To: Paolo Bonzini , Sean Christopherson References: <20ad6cd5-394c-d3ae-d99c-b656d7ef8293@amd.com> <20180821083911.GF24940@nazgul.tnic> <3d46f44c-dd78-8fa9-02ac-8206676ffde9@amd.com> <20180821151938.GA31212@nazgul.tnic> <92e2b80c-0dcc-94be-8d3a-5e11e5cf2370@amd.com> <20180822081417.GB4069@nazgul.tnic> <20180822150033.GA14200@linux.intel.com> <4d6ee892-a34f-28b3-18b7-1c663eb281c6@amd.com> <9635ebf0-7c99-6edf-1240-8dec28036a70@redhat.com> <20180823152907.GA1488@linux.intel.com> <60acb594-abe3-912f-9702-2f34961e575d@redhat.com> From: Brijesh Singh Message-ID: Date: Fri, 24 Aug 2018 10:41:27 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <60acb594-abe3-912f-9702-2f34961e575d@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [165.204.77.1] X-ClientProxiedBy: SN4PR0501CA0017.namprd05.prod.outlook.com (2603:10b6:803:40::30) To BYAPR12MB2680.namprd12.prod.outlook.com (2603:10b6:a03:69::29) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 0f2010ba-e464-4694-bfb3-08d609d814ad X-MS-Office365-Filtering-HT: Tenant X-Microsoft-Antispam: BCL:0;PCL:0;RULEID:(7020095)(4652040)(8989137)(4534165)(4627221)(201703031133081)(201702281549075)(8990107)(5600074)(711020)(4618075)(2017052603328)(7153060)(7193020);SRVR:BYAPR12MB2680; X-Microsoft-Exchange-Diagnostics: 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X-Microsoft-Exchange-Diagnostics: 1;BYAPR12MB2680;20:cH7TMaLSS6PjlnGHXsv5EyfhpNPZJ8AlMDT/xGT8U2801gLY5YPdLFdkWlNSPZspxGepPlRSrpdhDOsIZ4/wk4aPbg1BCGRySNg+aKPgpJ+C31+x5f9WEc/zZ1X5ddEueW2rDt9qqwfetZpYhp+qVZLzsI9/tpunRDZFONS+pPVTCC9x+fVu7QoULdtUPXz5Sd0NG8EKtkLNg2y4+LbvMP/gxrwS3DkOm7xTrqXX4Y+XJV1i7W6LDN6rJNy8KKO5 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Aug 2018 15:41:37.3273 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 0f2010ba-e464-4694-bfb3-08d609d814ad X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR12MB2680 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/23/2018 11:16 AM, Paolo Bonzini wrote: > On 23/08/2018 17:29, Sean Christopherson wrote: >> On Thu, Aug 23, 2018 at 01:26:55PM +0200, Paolo Bonzini wrote: >>> On 22/08/2018 22:11, Brijesh Singh wrote: >>>> >>>> Yes, this is one of approach I have in mind. It will avoid splitting >>>> the larger pages; I am thinking that early in boot code we can lookup >>>> for this special section and decrypt it in-place and probably maps with >>>> C=0. Only downside, it will increase data section footprint a bit >>>> because we need to align this section to PM_SIZE. >>> >>> If you can ensure it doesn't span a PMD, maybe it does not need to be >>> aligned; you could establish a C=0 mapping of the whole 2M around it. >> >> Wouldn't that result in exposing/leaking whatever code/data happened >> to reside on the same 2M page (or corrupting it if the entire page >> isn't decrypted)? Or are you suggesting that we'd also leave the >> encrypted mapping intact? > > Yes, exactly the latter, because... Hardware does not enforce coherency between the encrypted and unencrypted mapping for the same physical page. So, creating a two mapping of same physical address will lead a possible data corruption. Note, SME creates two mapping of the same physical address to perform in-place encryption of kernel and initrd images; this is a special case and APM documents steps on how to do this. > >> Does hardware include the C-bit in the cache tag? > > ... the C-bit is effectively part of the physical address and hence of > the cache tag. The kernel is already relying on this to properly > encrypt/decrypt pages, if I remember correctly. > > Paolo >