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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.onmicrosoft.com; s=selector2-citrix-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=OFe5AyKIYZ6R8ytjJFK0IlNDoqyNylHCztAikAkr3c8=; b=xKgBomUYK6K+uXR1tCW/PGlEBYMAVuAIN9NLHXj2HCUnBZUBfb7GqouJ3wcyIjGtRPVVGb7yCA5H7HKrWFD60CiIKlfGSpZM1FdTuhVMA+Ssml9XBd1GVVT4mYY5FLGjojMOgTdq1W95xIFllHN4SwAIqxXH+ol1TA/JVt0mZOw= Subject: Re: [PATCH 2/2] x86/cpuid: support LFENCE always serializing CPUID bit To: Jan Beulich , Roger Pau Monne CC: Wei Liu , Ian Jackson , References: <20210414110433.83084-1-roger.pau@citrix.com> <20210414110433.83084-3-roger.pau@citrix.com> <97d443b0-f5c2-0183-74c1-ab16d3cf1e7d@citrix.com> <63738788-c7ed-13f7-acaa-c1ad102442a3@suse.com> From: Andrew Cooper Message-ID: <84012b3b-9ed6-7724-8738-986570be6a44@citrix.com> Date: Wed, 14 Apr 2021 13:49:04 +0100 User-Agent: Mozilla/5.0 (X11; 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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?N2tTd1JaMGVMb3BPVUx0b3ZJampoMEhYekl5UXJEb1NOZ1FFWFVObkFrNm9G?= =?utf-8?B?U3pWQW16Q3hQTE9mamkwRHh2QWlzYjRSYmM5SC9jd3Q5eDI4N2dCRjNLa0xj?= =?utf-8?B?Y1JLcnpIMC9hd1hjcXphVTRvZkFSajRnNE9keGlVUXBZTUNrOWNHRWFPU3hT?= =?utf-8?B?LzA4SVZlTVV2WnRVRklCUlUzRFRjaGxvdHplbzkwR0dCMUg2eEpBci9TdjFq?= =?utf-8?B?cWoyWEZKYzkxbTEyOHp5Vm82bndVQnJMOG56dnNycFFFdmVJWitJREtIYkRz?= =?utf-8?B?WW0zd1d0RVl0MVR4ckhXbU5tUG0zRHgzTEJIckhibHJqQnNLWklXdytpdVBX?= =?utf-8?B?eVFWTXR2T2QvMEJxS1JZM0NSN0padFpRdXA4dGxVMHdwSkhOa0FDZ2FyelVt?= =?utf-8?B?S0lhdnlNT0lyQm4zekFWbWV5dWdzMlZSSmVySHVuTllyRnZrR29sQWxOM2tT?= =?utf-8?B?NVVCb1lmakl6Zk05ZEpBc2RwdXJUYTVIZ2hzM3dKaTFsTW01UE5HZ3ZZZVhi?= =?utf-8?B?RU1VQWY4WWx1QWovZXJlcCsxZVhGa0pEUi9lUzRIbXRPTU9sN0VWc0xtR01Y?= =?utf-8?B?eHNOd1hEelVNNVhXM3d2Mmx2ckxRc0Zhb1F1aFlvaUFjUllxSHA5UnBQK1lj?= =?utf-8?B?aGZQNGJjT29rRVluN290U1l3bVN1MGoyNmZ6bkVrVGZxRHpzVzZ2ZEZCRzVJ?= =?utf-8?B?dUdPejNIdFZnRDN5QnJxNElGYWhDZ1JvWGRVWkNyU0U5elN1MmZhU3FKM1hU?= =?utf-8?B?dnhuREpxWGlucWtJdlVDdHYwa05hQUZPMVBlbm45elF2M204bUViaWNWd1Ry?= =?utf-8?B?WVFjNHJvQ2lWR09PRzM0ZDlTemVkV29GaXFraFZTdmNMSERLTWo5UGJwcVNG?= =?utf-8?B?TDRzcnRXVWxZc2hyYTVJeXlYY2VSS2pXeGpwcHEwK3E1VGViM2pFVkdKb2Mx?= =?utf-8?B?OS9adVNEMndVQ3VwcW1uMy9QMGcvbFVVNkZFRktMMDRIOXlyMG8yWjRJQThq?= =?utf-8?B?QU1qTzVOT2dHemtrK0NOb1RxNm1lekZ6S0RKVmJRZURqNmlOd0VoMHZUUExi?= =?utf-8?B?SW54cWhFZlBzRm1wTzI5L0pxSkNWaHFubmhjR3NhMXpqQmxqQ3NMUms3TW14?= =?utf-8?B?VE5OcndENnVrQlNsM3lUc2tVODJxTTlXSC8vK2lMaGwvRUx5VzNiZWoxNVRw?= =?utf-8?B?NzEwV1RNQ0hHWDJMeGFIQUdIa3VZbE1tMG96WmdtVHpEcVpvbVJreE9EZjN6?= =?utf-8?B?V2hmZEhpSTdJTFJqRStteFVMcHRSbCtzckpwTUxjdWNSYUVRWjBNMFhyWHJq?= =?utf-8?B?dERLWmFCM3JMaEhqUGkzLzMvSzIxN1EreUZBQ1VDSUw4ems3M05xT2YzZWJL?= =?utf-8?B?UTg1aHFsTDhkMnpEQWxpQWlKQUQ3YXlaSG04VHRtZTRpd1VXdXYxRkY3ZCtW?= =?utf-8?B?aDVnVFRXdTRIdlo2alU5SWxxeUlPYlJjNTBzNnlSRGxBZkhLQWhrOThQOE5n?= =?utf-8?B?cnYza1RreldhT3NBWDgwNVhqb2tMZldORm9YMzdqS1ltZmU1Z0FSZGpCN1Fu?= =?utf-8?B?SFFmUnpkRkJ1M0lvanJkclFEUk1xWVpRcktrSWtmOVpVV3hWbnJzY0E4ejV5?= =?utf-8?B?YzN3VkhhcGV3TUxUQTRlTmt3cjV4SWlEdDViajVEeG9KS09GOGY2dVVvVEVJ?= =?utf-8?B?OFhuRXZTaExKaXVja3FSbmMrWEg5bm1ocXZUais2TDI2dFJMRGJUY094dTY2?= =?utf-8?Q?aRFZvM6naNv5vrSi5+y8at7MES4REVhW9vkUdvx?= X-MS-Exchange-CrossTenant-Network-Message-Id: 935a22d5-2435-43c9-f7cc-08d8ff43b316 X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB3623.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Apr 2021 12:49:10.6793 (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: qixzGALB+dgCI3uVDke+tmF0vtoHAgWA+LRVUysW7yYy3BQ2BDcGNgPJh7k9jZcp01166D6i/RbZMh4a0nCkI52al/eMw7mwz8wX0qYzoe4= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR03MB5439 X-OriginatorOrg: citrix.com On 14/04/2021 13:45, Jan Beulich wrote: > On 14.04.2021 14:33, Andrew Cooper wrote: >> On 14/04/2021 12:04, Roger Pau Monne wrote: >>> --- a/tools/misc/xen-cpuid.c >>> +++ b/tools/misc/xen-cpuid.c >>> @@ -178,6 +178,11 @@ static const char *const str_7a1[32] = >>> [ 4] = "avx-vnni", [ 5] = "avx512-bf16", >>> }; >>> >>> +static const char *const str_e21a[32] = >>> +{ >>> + [ 2] = "lfence-always-serializing", >> This is a bit of a mouthful.  One problem is the fact that "serialising" >> is an ambiguous term, because neither Intel nor AMD formally specify >> what it means in the architecture. >> >> There is a description of what "architecturally serialising" does, which >> does occasionally move over time, and the name of this CPUID bit in the >> PPR confusing at best, because it very much isn't "architecturally >> serialising", and the term "dispatch serialising" isn't actually defined >> anywhere. >> >> Intel have now started referring to LFENCE as a "speculative execution >> barrier", but this still doesn't have a precise definition. >> >> I'm afraid I don't have a useful suggestion for something short and >> concise, which also conveys the precise meaning. > How about "lfence+" or some such? Hmm yes - for xen-cpuid, that's probably fine, and for churn reasons, we can keep X86_FEATURE_LFENCE_DISPATCH which was the best name I could come up with at the time. ~Andrew