From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from CH1PR05CU001.outbound.protection.outlook.com (mail-northcentralusazon11010047.outbound.protection.outlook.com [52.101.193.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 99B1A38CFFC; Mon, 2 Mar 2026 09:36:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.193.47 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772444187; cv=fail; b=lnSLQsLHWC2NWw9NLBLmqfPV6Ahuo8T1vmHHCsqZthnadlW36pa7E50nBVK/9eGUQFrNe64ykLOiYUwZGw/nhFD8kk9vOrZOUDv4QvohBepO9lpDN/rxt/5UIdu9DdJFEQHp8CdGCv3tiEovW2EU3KVAcptVoeCOyZNf2WrcVGY= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772444187; c=relaxed/simple; bh=okvmapAr86ECPikhfDjhpQza2YuMYkhQabQ1QdZoxd4=; h=Message-ID:Date:Cc:Subject:To:References:From:In-Reply-To: Content-Type:MIME-Version; b=imb4FxakIaUtC1BxDIx1hqRpzdiB9sfisZERJyhzg8lFI6FDUIlsec3IZXJVViftRPPAIeghWwY6SKP1oDG68jebWcNmeIFDbYSLpsAUm2CsZU40tE4ItTB83m5bOZZqsAm8kt9/d3863iGZuaRMlZPFA9YbmEf1TMhluNd8z8A= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=citrix.com; spf=pass smtp.mailfrom=citrix.com; dkim=pass (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b=cjoozq8y; arc=fail smtp.client-ip=52.101.193.47 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=citrix.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=citrix.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b="cjoozq8y" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=R9TbWfUOQrQ18+CHFG/FxQ/l8AgkCsVwBlGnEkj/vODMALUijnlq/UcKDFVRPJMe695BYWtkwGtP7dGnD3gu4WHLiki92+wGncPeNQrwFxwWeDHZi3Ui6btNvKrNVuXmg09Wz+pr0JJJ4rjXsclfgdOBeKwSYJRiwWKo3xWMREJ9APUYplC1j8wTkmeCgYmeFgJ646fTEuGkUcevdp7LA5bp8zm2aISaw1I/fbiOZPnpiGnFi8fEoAI7BNImVmAZs4PXuyESARScHj2D5rQhvp2lUzNjWSb6Jo/+feJjgmMa6sI4YF7PXyZ0aLouSawwHQyQLLFI30WuTKhG3SFdLg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=+8NLqrhrvJGe10958GB5hFrE5LoWWzgJqJf2n7mpkBA=; b=BIQgcaNVwiBO3ImhqXxLVkcW/G6KY3qTxMEwRErJSY+sd+tiMjnALquoRw96nkIGpptUKQmQog/Ly9GwRs4VyHgqKEVRBJ7yDqD6eJs5eWpnZOIS3ZOFrTXfSaJXInt94CF28Lt9GYIb4/yvRM94oi1yIjjfB5ZM3jmv8f91DlS7nlHR/oRWPmFKKD+pwXA9C0XnkC4RdicyqAGDV4NejgMc14t2bPzY+Tqx/e3RpQSRl8h930N3mGirqc+pfBIc3mnslpz/QoC1GCT+moj6H+cdzWLbtV0DfUbmf/Rzt+SWHEna6yHK+i8YmSkHFWfDA9FJ8oh04igNMEV6qfiSHA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=+8NLqrhrvJGe10958GB5hFrE5LoWWzgJqJf2n7mpkBA=; b=cjoozq8yghsP8LibWLp36P47clqheOnCIcViuw0AmUdnIYa3NoteVqDKajQgs5q1DqkeRN5iFT69hfP7Y4jjT1lvM+zMQD4plRHXOekvhDDCP67aDfLg0HLGQbUPJSn943TeHOnzCJzgZj9ekrNMfPsfiT16tbfx0RlPYuoTnPg= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=citrix.com; Received: from CH8PR03MB8275.namprd03.prod.outlook.com (2603:10b6:610:2b9::7) by LV8PR03MB7493.namprd03.prod.outlook.com (2603:10b6:408:185::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9654.21; Mon, 2 Mar 2026 09:36:23 +0000 Received: from CH8PR03MB8275.namprd03.prod.outlook.com ([fe80::a70d:dc32:bba8:ce37]) by CH8PR03MB8275.namprd03.prod.outlook.com ([fe80::a70d:dc32:bba8:ce37%6]) with mapi id 15.20.9654.020; Mon, 2 Mar 2026 09:36:23 +0000 Message-ID: Date: Mon, 2 Mar 2026 09:36:20 +0000 User-Agent: Mozilla Thunderbird Cc: Andrew Cooper , x86@kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] x86/cpu/centaur: Disable X86_FEATURE_FSGSBASE on Zhaoxin C4600 To: Yao Zi , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" References: <20260228173704.62460-1-me@ziyao.cc> <05f84fa5-d0df-4bab-80a6-5ff2c418b5ec@citrix.com> Content-Language: en-GB From: Andrew Cooper In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: LO4P123CA0053.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:152::22) To CH8PR03MB8275.namprd03.prod.outlook.com (2603:10b6:610:2b9::7) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH8PR03MB8275:EE_|LV8PR03MB7493:EE_ X-MS-Office365-Filtering-Correlation-Id: 57cc2671-b5ab-421d-d4dc-08de783f2b10 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH8PR03MB8275.namprd03.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(376014);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?REdIclg1QkFHM1RXdkd6OXpqcG4yeVZtTndIQmRNcVNTbE53bEtzUU1jZnhC?= =?utf-8?B?ZlptR3BEUENNZE5LTkd2c0dRNStwbm5leE9hR3BHRmJJMFNIdGZlZ3pNdi9S?= =?utf-8?B?djdZRmN6d2FRYTRvUGZycDZCcDVHQXRnRWxNUlQ4Q0ZzYzd0N1J4dHgwWHBl?= =?utf-8?B?R05EVDVxRTZMZEhJZzJmV3dna0hmVHgvcG9IRk5KSDg1cGI1cDc4L3diS21p?= =?utf-8?B?Mm5UbmRkNHlLYjFOOTZnQkxybU5ZTnhwS2Y0bTFSbjBaRFREbWNGa3J1eWx5?= =?utf-8?B?TlMxYUM1NjhNeS9WR1dGblRJM1dFMVgvWGNyTzZsQXROdUhESnNEdURrcUZO?= =?utf-8?B?SVV3UFlmdUdzaGJNVVFVaitZbTJSN0JoYWFoRWc2WmNoMXA5SnZnZTc3U3My?= =?utf-8?B?N29sR3JUTkl3YjZWTTRTTU5xUmUrVlRUdXBiNmFXVENqTGVEWUZDMFZJTk0z?= =?utf-8?B?VDhaREV1cXpiNlNzMmQ4dWlnR1R0MFBGaVVWYVVxT2t5RWVlcVlNaDhkOWJt?= =?utf-8?B?dGtsdUJjT2tPQ1pTK1Ezblp5ajFUVm9lT0sydWplbWFTTytYaWpSN2dDcy81?= =?utf-8?B?ZEw1N2Y3MkpvSkVITjJaYWNSZEVISmVnM0FCWHg5cjR5Q0U1Tjk4aUFSTnFY?= =?utf-8?B?ZUYxeFJNSjJkUmpmejdHa1M1ZU5pUG1PbUpHb1REaHFOVlV3dnhqK3FtZEc1?= =?utf-8?B?N0hXV2ZkU0o1MUxaK1QrME4rL3R5VTBJTGpzNFBVUm9HTVZ2blBzemNRT2RJ?= =?utf-8?B?T1BPNG9oL1FJR1JEYy84cTMvWXp6a29nUFZ1eC93eUFrU2xobU00Wk1DSGFQ?= =?utf-8?B?dHFHZDRwV3JLdVh6dTJwR3NLckJzVUZuQWRQRUVBY0k3ZmE2SXQ4aFl5QkZN?= =?utf-8?B?MWJ2YXN5M3M4QXpZS0dUZ3d4RGYyeWt1akFoSFV5NXIwV2VDR0dmTDE2d0Na?= =?utf-8?B?OWFIRXJPbWppWU1HQTRXTFZmWEJMeDFxSncyaiswbmQ4by9uMlBBUEFlclFv?= =?utf-8?B?WDZhS2lGcTBVdVMwR1A4eTlScVNNVG1UODBFTTNJQk1IUWgwcFp4MTFyNkt5?= =?utf-8?B?N1ltY0orc2xyQmFOdWtZRVowMTQvaW00OW92M3l1aGhlUjNKR1dJTFhGL1J4?= =?utf-8?B?TzRhcHh4ZCtQK3NNKzRRampSbE9NRENUUTRFdjlZRUliZ1NEMGNPWkJ0REwv?= =?utf-8?B?SlFxRDJ5M0JvY0VPZVJqRFZIYXJyeWxjdDJPNkdLUml1NXo0OFhrcHJvUDlT?= =?utf-8?B?M0Q4aFdNMDU2a0VhdWpxQmFSQk1LUHZpbmhOd2pjQ00wNll4YmVoVm5BZnk5?= =?utf-8?B?RkJhT2VRb0c3ZXN2MCtjN3pTOUFPSWhJWllHL0pzN2JlSlZrYk0vbG5PVHRL?= =?utf-8?B?RDdMcFllOGVwemFFcG9nTW00YjAxVjlPcEFhclg4dERnYzk3THdoekF2Um12?= =?utf-8?B?eGNpbm5lRG41K0JUUityMWR2cHJLcXBXZGNONUpzVGdhWkFuQjMrQVp4Qzky?= =?utf-8?B?MTczcG9jZVdFaTdKUCtMaGVIY0trZ2c0emd4L3lWMVZpTlErMlFvRTdpWG4x?= =?utf-8?B?MVNOOWpMcWxUS2lpc0tzaVdoV0p5NTFTSk1JdWltN3BnWjEyWjNyT1BxcGRK?= =?utf-8?B?MVg1Z1ZTeCsrVkZxRysvN3k2UXpESGxrNWNqSFdZVTNmTFBFVDJYaG9ncURq?= =?utf-8?B?dDdVYUJEV0lkMVFndDdCeDBsSlk5aEZtV0ozWjc4RzltNUtqcHFIM0F6eFZj?= =?utf-8?B?Y09QK253a1FRL3oyc241d3BwQmJwbnpPaVJ3akZaMlBIMkxlR2M0aWlKdm44?= =?utf-8?B?VkpBamRMS0VlWUJlWE1wT3VVblk2cHJNMnowemxtbUdCSzVtWnF2QTBRTzFB?= =?utf-8?B?V0dZRURGN0k4WHMzWmdNRVd1YXMxL2dScHQ0MjNzS3hCL2tod21WMnA3dVFW?= =?utf-8?B?VUZ3Q3NjekpHMXpDL2VaTENtNzRwaWUrZHJZMUgrM0p5eFJoZzhTSFpKMDFp?= =?utf-8?B?TnMvUVoxdE82bGVLQlNERE5lSG5DNWZyYStPN2R5eFlURUdFblNUdDg0dXFN?= =?utf-8?B?enkyc0FFV2djUURNRXZVbFVOYUw2V1QyMEtXR0FYcnZhRG5KaDlYNTJsVmpj?= =?utf-8?B?VnRjemZoeUszNGZIOFlyS3Y0VFJXc2VuUmY5Vkh4aUtKOVZvL3FlcTFnRk9O?= =?utf-8?B?TmZpWUlmS0VHWWN5K1VscmRwK1lTS3E1MUhFYWMzK3lsZ1hyK3hDVWxUMHBl?= =?utf-8?B?MHpzYTBwS0tBQjZQNGcvTTl0bmpNZitYdVlZbXlkKzlRYkduaXlLR3VHajFG?= =?utf-8?B?Vm5HSllIUXk1WC91Tk81TG5vTTNGREduVSt6N09xVnZFZ2pBbHNpQT09?= X-OriginatorOrg: citrix.com X-MS-Exchange-CrossTenant-Network-Message-Id: 57cc2671-b5ab-421d-d4dc-08de783f2b10 X-MS-Exchange-CrossTenant-AuthSource: CH8PR03MB8275.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Mar 2026 09:36:23.6494 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 335836de-42ef-43a2-b145-348c2ee9ca5b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: YQlNFyk4Iaqgo1269FE2kqmbT/p55HdN9Jdte3lrW/5IQuHDgApOIFu13ZQHRNkWAkDTyaGUiV3UkxB/EPjCA/5iGnKmjMhOLAlf5fk5T8U= X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV8PR03MB7493 On 02/03/2026 5:08 am, Yao Zi wrote: > On Sun, Mar 01, 2026 at 04:29:13PM +0000, Andrew Cooper wrote: >> On 28/02/2026 5:37 pm, Yao Zi wrote: >>> Zhaoxin C4600, which names itself as CentaurHauls, claims >>> X86_FEATURE_FSGSBASE support in CPUID, while execution of fsgsbase- >>> related instructions fails with #UD exception. This will cause kernel >>> to crash early in current_save_fsgs(). >> #UD is the expected behaviour of the FSGS instructions if they're not >> enabled. >> >> Are you saying that this specific CPU enumerates FSGSBASE in CPUID, and >> permits setting CR4.FSGSBASE (without #GP for a reserved bit), and the >> FSGS instructions still do not function? > Yes. Without any workarounds, the kernel crashes in current_save_fsgs(), > which is the first use site of rdfsbase, instead of identify_cpu() where > CR4.FSGSBASE is set up. > >> What happens if you read CR4 back after trying to set the bit? > CR4.FSGSBASE is set correctly, I wrote a small patch for testing, > > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c > index 1c3261cae40c..d89a2cc71147 100644 > --- a/arch/x86/kernel/cpu/common.c > +++ b/arch/x86/kernel/cpu/common.c > @@ -2048,8 +2048,13 @@ static void identify_cpu(struct cpuinfo_x86 *c) > setup_lass(c); > > /* Enable FSGSBASE instructions if available. */ > - if (cpu_has(c, X86_FEATURE_FSGSBASE)) { > + if (1) { > + pr_info("%s: enabling FSGSBASE\n", __func__); > + pr_info("%s: before enabling, CR4 = 0x%lx\n", > + __func__, native_read_cr4()); > cr4_set_bits(X86_CR4_FSGSBASE); > + pr_info("%s: after enabling, CR4 = 0x%lx\n", > + __func__, native_read_cr4()); > elf_hwcap2 |= HWCAP2_FSGSBASE; > } > > On BSP I got, > > [ 0.298016] identify_cpu: enabling FSGSBASE > [ 0.298021] identify_cpu: before enabling, CR4 = 0x1200b0 > [ 0.298027] identify_cpu: after enabling, CR4 = 0x1300b0 > > and on APs, CR4.FSGSBASE seems to be set by default, > > [ 0.414981] smp: Bringing up secondary CPUs ... > [ 0.415211] smpboot: x86: Booting SMP configuration: > [ 0.415219] .... node #0, CPUs: #1 #2 #3 > [ 0.001869] identify_cpu: enabling FSGSBASE > [ 0.001869] identify_cpu: before enabling, CR4 = 0x1706b0 > [ 0.001869] identify_cpu: after enabling, CR4 = 0x1706b0 APs inherit their configuration from the BSP. In which case your checking logic wants to enable FSGSBASE in CR4, probe a RDGSBASE instruction (see wrmsr_safe() for extable handling), and clear the feature bit if the instruction faults. This will be far more robust than looking at the brand string. ~Andrew