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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=Ud91ZUGiELp7dK+WvV+JKkvJnwquss6sCLbZsKcKllQ=; b=IIX+gUvQrJ2ukCxiXLGfmOOQKo7TRo5GBaoBQ9MvpwF9rS9swoEZoH4qHtb4atj4eqys0DtbdIcqFB+o9iXUSNtau0Tj7D6vgD4gcZ8+gSLb1t8PG40vVcm5P5vnpzfZ6ea5ayjb5IplNozwgTJww2pQI09BT3WaPnOnW54zfU8= Subject: Re: [PATCH] VMX: use a single, global APIC access page To: Jan Beulich , "xen-devel@lists.xenproject.org" CC: Kevin Tian , Julien Grall , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= References: <1b6a411b-84e7-bfb1-647e-511a13df838c@suse.com> From: Andrew Cooper Message-ID: <3c7a4cff-3f11-22e1-ed46-e76f62cc08f4@citrix.com> Date: Wed, 10 Feb 2021 17:00:18 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 In-Reply-To: <1b6a411b-84e7-bfb1-647e-511a13df838c@suse.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?SC82NmVEd0RQS3Q4aFVUdzJDUmVrckE1WFdxSHJhZUY2UzVNeGxOYjByQ0Nq?= =?utf-8?B?eTNSdWJEQ2VhYU1yTWZweXVlSFRiVkRuaFJrWnJVWnZ5TmFIakZJTUhndHA5?= =?utf-8?B?QkdjczUyc0JObS9GZE40YUl3TkVVK3lqbXU2alZneGpadnB5YlhFYmd4MW01?= =?utf-8?B?S3Y2K21VNEtaQTNBU2xjWmNQM3ZLN2kzSDRIaHRnOTJIK3FCZTFRZkFDUTZm?= =?utf-8?B?ZlRlWGhseDBmNEJLazFLQURRd3lERm5KN2crOFZrNlNyQTJtWjJ2MXhFdVFw?= =?utf-8?B?cW82VThKakdoS28reDRwSG5aMzY5Vy9OY2hZc21FWlBBWDdQREU4MDMvZnJp?= =?utf-8?B?MTdhU0ROWEtZNTV2dTUzUVZ1SVYwalp5Q0JGTTNtMjh3emVIdnNwbzhTdE9p?= =?utf-8?B?WmVqSDFMZ2tZUmRZbjVwb1pBb29STWlOM0RieCtjZGl6S2JIU3MvVjhMWCtO?= =?utf-8?B?dGxRODJCQnJ3TXk3aSs1N0ZSa29UM1JlZGt5bGVtNWRXRmg3RWdkSHozOEpr?= =?utf-8?B?S09SQ1ZQMThVSjJpS2JSK3VEMXNGVHY3SXFtc2pYaG81Z2NYZHB1NTBoVkxW?= =?utf-8?B?b2YxdGNUdWlRbnBVUVVkUE9naFk4MnhCRW85QkNDYi9JNXpCRHVpanhOWUtr?= =?utf-8?B?cmRlRG5GVDdkK3FmL09LYnZ6VGJUVG9PUGlpdGlaajd1ajFrcFI5UGt0MEpU?= =?utf-8?B?NGo4czhscFZqUUswc3Y1NEVSbzZxY2R0Rmo2UnUrV2dOTHFtaURsU2RuUkZ2?= =?utf-8?B?enEwYUI4Ykd4Z044eU03QjNtZXJSeWhLZlNzU2pXZ0tVTEV1VnQ3TnY4VXdL?= =?utf-8?B?UW9ubmMxUEcwS0lUeElQWjVLbThjWnNFU1Z3Y2hXVU9QZkRZV1VYUUpiejFE?= =?utf-8?B?ck91dXhrakVTeHhyY0NVQ2NYK3BIM0tjZ0RzZTVwMDJCSlFjdTFlVGVjcFhW?= =?utf-8?B?enBMR1BPYW8vanZHaExadkY5VHZMc2hvZHVZY0ZWMFNCQ1JFSTBFa1pPbmxE?= =?utf-8?B?VmkvUkFCcTFZdEtUb21ubzVLUm1DUTBNVWUwOTZ3bVFwZUpPVjRURjh2R0VC?= =?utf-8?B?bU9Sc0twK1ZodldMY08yQXlLcVNMVVBaVHJWbmlzbzIzdnIza1c0NVlhQ2dY?= =?utf-8?B?TU9TWTR2ZlpIcy9zeDBGZUI3MmNVd0RYK0pyZUZ1OFg1dkJ6QVhSTDE5VW1D?= =?utf-8?B?Z21PeWlBVTVXNDVkVy9QT1VqUzBRTTFGTXFyTmNUSEJnOEJ3TVJUSy9EWHl6?= =?utf-8?B?eXNEeEY5M0IwQmkxcG9URmk3MW5hdTByd2VtN2lRYzIzay91KytFRU5QSTJ4?= =?utf-8?B?YVR5b3lkMStZN1Ivb01WU2Q1RnUvNzl0VGdYRDAvTmZ0dU5ua2NoNjB3YXJh?= =?utf-8?B?QkJXdzdNMjljRTVkTWVzMElGYWZVWmlscEsxQ1ovT2VabzNadUgzQ2Q1VUsr?= =?utf-8?B?U29yZWNtYWlSYkI1dkZmRFAwUjM1SkY2YWV2NGtjdVVWQXJ6ZHB1SHNLZVdT?= =?utf-8?B?VE1iSkFyVUQ5M080R0hkVG4vaFlWN1o2MXdYQ0tSZlVYQUhyZFh5Skk2dGdx?= =?utf-8?B?cnFlMkFIZHhXTWtHeWxJT0VGejBPMk56dktVaVo0eklhRUgzV2ZJTmVGeVdD?= =?utf-8?B?OFRqbFpKaUFDUG9jV3RzS3hrK1FpaHJ5dnNsSWZkdlJmcjBkdGpxcUZFZGVM?= =?utf-8?B?dE9NTDBzVjZIWEcyb0ZocFBnZjMwRXo5bm5BemI1MWtJSkFXOWcxT21Qa2VT?= =?utf-8?Q?iI+xYPoZXYrbokYbWkbIXXkw8vB84QJW6RMjYpf?= X-MS-Exchange-CrossTenant-Network-Message-Id: 3af7927a-e94b-41b8-f010-08d8cde55bd5 X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB3623.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Feb 2021 17:00:24.6786 (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: 8NtFszymuzEkAWWV0rkAV6xYxeM4XSbEUzThQ3jHIUm0p/HzDSiznSYfmOKf0YDHybw+TvoZfk991W1oZgYtLod9sF1v53B/qpedj1ejvzQ= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR03MB3558 X-OriginatorOrg: citrix.com On 10/02/2021 16:48, Jan Beulich wrote: > The address of this page is used by the CPU only to recognize when to > instead access the virtual APIC page instead. No accesses would ever go > to this page. It only needs to be present in the (CPU) page tables so > that address translation will produce its address as result for > respective accesses. > > By making this page global, we also eliminate the need to refcount it, > or to assign it to any domain in the first place. > > Signed-off-by: Jan Beulich How certain are you about this? It's definitely not true on AMD's AVIC - writes very definitely end up in the backing page if they miss the APIC registers. This concern was why we didn't use a global page originally, IIRC. ~Andrew