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Bae" , Thomas Gleixner , Sasha Levin , Borislav Petkov , Peter Zijlstra , Ingo Molnar References: <39d57e4d-5db4-f536-6f5e-6b0414c0dccc@amd.com> <7dedb0ab-56a6-5d96-577b-21ab1ecdad24@amd.com> <20200820151049.GA26595@sjchrist-ice> <362f5a45-b808-25ad-b99b-449e05717c4a@amd.com> From: Tom Lendacky Message-ID: <45e16c5c-ce99-33da-99c8-ea52ef0945db@amd.com> Date: Thu, 20 Aug 2020 11:17:00 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SN6PR05CA0030.namprd05.prod.outlook.com (2603:10b6:805:de::43) To DM5PR12MB1355.namprd12.prod.outlook.com (2603:10b6:3:6e::7) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from 255.255.255.255 (255.255.255.255) by SN6PR05CA0030.namprd05.prod.outlook.com (2603:10b6:805:de::43) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3326.10 via Frontend Transport; Thu, 20 Aug 2020 16:17:01 +0000 X-Originating-IP: [67.79.209.213] X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-HT: Tenant X-MS-Office365-Filtering-Correlation-Id: aefbc303-6b9e-4149-ef5b-08d8452478ca X-MS-TrafficTypeDiagnostic: DM6PR12MB4355: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:843; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: FkTyG6j7JchvqxVp0suMq9QQ52UbkN76Zb1hrQHtiQE57SQ+YJ+RcjZXXXQHi3xnXXT9P0nDyg0Ngind+kp1dqRS8YZRtRNppavlZO/5AkVkLS8empI3mODlVTUv18OkrPEKo33mfI+TeYGkw25q4og9p/K4L4ucJ+OowmVfZz7pqOzardZr27LYkRFdkiaG2vXyoInS43LcH4sQ2oIk48HQeOiPS4GRYeW7BH4PGVqGY+6BRdfMMnAAhRfObYHJvXHzEgBeNaoL2ocejsbaFO9xio2cShYqMjHxZSU9acXgNkaLji4J/t5PZagncVDXxkHOft1PwKGaYTR2glRp1AkzJWM0nPkP54j/f1fpUcJQHsGKzYxAboKVF4G8Q4wGWFouPFKsTrb15n4zTl2lFbQ5RLmHRP0uuuBgIl9G9Ec= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM5PR12MB1355.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(376002)(346002)(396003)(136003)(366004)(39860400002)(956004)(2616005)(31686004)(6916009)(110011004)(2906002)(8676002)(52116002)(4326008)(26005)(54906003)(36756003)(6486002)(86362001)(478600001)(16576012)(186003)(316002)(7416002)(66556008)(66476007)(66946007)(31696002)(5660300002)(53546011)(8936002)(43740500002);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData: lQ2oiZSkxIOvx4/sGfWtyumlX5gSTZesMrr3SMrQuntnvzWQHx1YFdCB/yU4EnQZTMkgCrDygw8VCBjDRmYYvx8XgJhpbm3GUw/JdJW0Ny0hpFZB7d5cH7k3nVV9JMOV3H+LS3aWegKwMsx/4zE7gINJSWOClddPD7GLqaxVMYlAP0RybI4N+faVpogeXIxtJRCBR6imGMfcC7s82twyLQKKmfw2FEwBsEDqGmMrfImOWKfwnScvOKho/sPbn+4HwU4WXD6N820HzHIrQm8nJwwW51vm/TwifS2lbJmWYoNdPM3KQk+dbNV118fY06ro7R1Ssh6NaAHoDIe5wWIZHR+A/5FRps93s0E6/lyQo3JT+VNxVA3UPdjdnhxu/IuFEC/PHM/ZXLGXLk0CwFKY/7MDjeQpEefOsHctTnuTfmE9DQkiFlRXxEqIhVoKp87U5WeKmfs/5wDVnny3y2Rp6YbIhIqUxuV6EhOnRYk5DrEU5t8SdPfGPkKOj0QAiV2LjrKarkn+CvOWY9nDy5nqL5jjBubVap2yllKvCi8c4TOLQFh7h3F1BGBpiqfCnab5dO1rhP9NH4z84Bix1i6/7lw1+oYmijofQRLGQ5bdi0vVJ5a8lh5ZkhDDb9i/r0rvpHj3AspJrOEMqPUuxQbebA== X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: aefbc303-6b9e-4149-ef5b-08d8452478ca X-MS-Exchange-CrossTenant-AuthSource: DM5PR12MB1355.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Aug 2020 16:17:02.2539 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: AZH8ubKDfyWBdr7XmxOkv4x0RTjBOjRqCTzVaxj/Hk1psBbIg8oKOqP0zuQtkxzgzPemQCuoczaMV6OcwV19TQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4355 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/20/20 10:55 AM, Andy Lutomirski wrote: > On Thu, Aug 20, 2020 at 8:21 AM Tom Lendacky wrote: >> >> On 8/20/20 10:10 AM, Sean Christopherson wrote: >>> On Wed, Aug 19, 2020 at 05:21:33PM -0700, Andy Lutomirski wrote: >>>> On Wed, Aug 19, 2020 at 2:25 PM Andy Lutomirski wrote: >>>>> >>>>> On Wed, Aug 19, 2020 at 11:19 AM Tom Lendacky wrote: >>>>>> >>>>>> On 8/19/20 1:07 PM, Tom Lendacky wrote: >>>>>>> It looks like the FSGSBASE support is crashing my second generation EPYC >>>>>>> system. I was able to bisect it to: >>>>>>> >>>>>>> b745cfba44c1 ("x86/cpu: Enable FSGSBASE on 64bit by default and add a chicken bit") >>>>>>> >>>>>>> The panic only happens when using KVM. Doing kernel builds or stress >>>>>>> on bare-metal appears fine. But if I fire up, in this case, a 64-vCPU >>>>>>> guest and do a kernel build within the guest, I get the following: >>>>>> >>>>>> I should clarify that this panic is on the bare-metal system, not in the >>>>>> guest. And that specifying nofsgsbase on the bare-metal command line fixes >>>>>> the issue. >>>>> >>>>> I certainly see some oddities: >>>>> >>>>> We have this code: >>>>> >>>>> static void svm_vcpu_put(struct kvm_vcpu *vcpu) >>>>> { >>>>> struct vcpu_svm *svm = to_svm(vcpu); >>>>> int i; >>>>> >>>>> avic_vcpu_put(vcpu); >>>>> >>>>> ++vcpu->stat.host_state_reload; >>>>> kvm_load_ldt(svm->host.ldt); >>>>> #ifdef CONFIG_X86_64 >>>>> loadsegment(fs, svm->host.fs); >>>>> wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gsbase); >>> >>> Pretty sure current->thread.gsbase can be stale, i.e. this needs: >>> >>> current_save_fsgs(); >> >> I did try adding current_save_fsgs() in svm_vcpu_load(), saving the >> current->thread.gsbase value to a new variable in the svm struct. I then >> used that variable in the wrmsrl below, but it still crashed. > > Can you try bisecting all the way back to: > > commit dd649bd0b3aa012740059b1ba31ecad28a408f7f > Author: Andy Lutomirski > Date: Thu May 28 16:13:48 2020 -0400 > > x86/cpu: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE > > and adding the unsafe_fsgsbase command line option while you bisect. I'll give that a try. > > Also, you're crashing when you run a guest, right? Can you try Right, when the guest is running. The guest boots fine and only when I put some stress on it (kernel build) does it cause the issue. It might be worth trying to pin all the vCPUs and see if the crash still happens. > running the x86 sefltests on a bad kernel without running any guests? I'll give that a try. Thanks, Tom > > --Andy >