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Date: Tue, 10 Feb 2026 08:54:13 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Alejandro Vallejo Cc: xen-devel@lists.xenproject.org, Jan Beulich , Andrew Cooper , Xen-devel Subject: Re: [PATCH] x86/hvm: short-circuit HVM shadow guest creation earlier Message-ID: References: <20260209144049.86535-1-roger.pau@citrix.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: MA2P292CA0018.ESPP292.PROD.OUTLOOK.COM (2603:10a6:250::8) To CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH7PR03MB7860:EE_|DS2PR03MB8157:EE_ X-MS-Office365-Filtering-Correlation-Id: 2624e2c7-7493-4c77-6da1-08de687996e0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016; X-Microsoft-Antispam-Message-Info: =?utf-8?B?WFJDSzd5Nm5DWWpaS0oyN0w1RlhnMXY2MFhTMWRHUmxxZEVTNWozMUhjS1FX?= =?utf-8?B?Y2lGKzhOQmEvbUlZMjFZKzNTZytERUVJaHB2MnJmYWJXNHVuaUpIalpmVGE0?= =?utf-8?B?d1QxMDRqSnFzVWU5RVVUdXM5YlY5b056SUxJM3ZhYjNGOHhYblBHQi9ZNWtG?= =?utf-8?B?REwxR2J5UnBTNkcrU3UyZjJNSmt0T0gwQ0NqSzc5ZzlBRmtCcVFQSzhZdEEr?= =?utf-8?B?dU9DV0ZVUXJFMFAxVVkvVnF1ZDcxaXBpT3ZRLzBQWWNJR1ZXaUw2TjJQdHdv?= =?utf-8?B?VGRsL0w4b1l1T29MQUYwTkdnVzVNU2s3SkorU1RHNTdCYkF2cHdDUVFtZHR5?= =?utf-8?B?RzRkRGVxTGNLMjlmNkY5d3gxdjUycW5oK3hUZXJFRzVISjFDclMrYnVVTGo2?= =?utf-8?B?YlFNQnFWV2Y4ZFc4L2RiRGs0ZDlkakg3YXJ0NHN5Q29jQmMwWmF4LzVWcERH?= =?utf-8?B?b3Raa3h4bVFWK2JtTHg4djVoUUJEZ05wTHh2aGViWXhRYWpWeHZrTmI2UUlI?= =?utf-8?B?aGduWDQ2WDdMZ1lseUNidlZmTGcwL0pyVUp1RkZEQnZXWXVNcnhmQWtJQmxY?= =?utf-8?B?YjJDNkIwWFlEY2FtNUh1NXp2Q1l0WVVmRHZtSXM1WjNmRmk1NW5rS0Z5enhw?= =?utf-8?B?VEN0dHVlT2JRQ0UxV21mbWVQeTVZTVhaWVlOM0hoT2E5Um5SZmxSTXNoSFMr?= =?utf-8?B?V2h2eTF6ZW1sRzR0NitzWjhEbE9sYS9oSUZ6amx3YUlWdmF0Smd3TkplYm9H?= =?utf-8?B?aVRTTmsvcE5aa2d4d29QMWlrTGZqK1h6ZHRxRitaWEhrVzdCcXVET3orRE5P?= =?utf-8?B?YkZlVm8xSVRucFErNldhdzhrRUkyYmgwN281UW10ZGpPaktFQXI3MG1rbXNo?= =?utf-8?B?S09VMGd0Zjhzbmcvdlc5UnhZQW8yS2dISVNOSXpwSVFTbmJhK0RUL2FrK2Q5?= =?utf-8?B?MU5SWS9iSFluekFwem1HWHVYMXYwaUhzSFpKMWs2NnVZazJMV3hTTzhNczJI?= =?utf-8?B?SC9NamhaRENlcFZqaDJwdTl1T3N0ejd5RXJydmxYL2FIbHR0VHN1L3k1emcr?= =?utf-8?B?dnBmUzE2TzJNNXZOazB1eDZrZVhlRTdqamcxbS9Xa0R4ZHA4azFqTm9YSWQ4?= =?utf-8?B?RzQrTnJvYklvY0dSdnZwcDEzeGdwdTYxamRyayt0Um1LSXBiTGdzK2ZyaHJV?= =?utf-8?B?eWJNRFhFT2l2YWw1UWtlaFUva1A1YTdkcnBzbkpLWkJPeDRmTnYxeFV6WWdV?= =?utf-8?B?WlIySmxQdHhDWTdlZE02SlcwUXlNZ0NXcnNlYUVsZ1djWnh3R1cwSW5rRGZX?= =?utf-8?B?RHJGbnd2V0V0NU84NU1kN2x4KzlvODV4aHRxMnpUelBBb0tOVDlNUkZIbjJS?= =?utf-8?B?TjZIZ0tWak1iSFVqL1BQbExpYytIbEx2WTMwc1RFaWRVS0NEQXFPbk9Gb0p0?= =?utf-8?B?RVlaem5NVE1KTXNpMHJ5UmxUQlR5bkdEeW84Y1dKa1MxbVgyOGdTOXhBeUNF?= =?utf-8?B?cTI0eitJQWhrMHhKdTg3WVRVSWNkeFRwWGNRSmhoRmpiTVNNdllEUXdmVitC?= =?utf-8?B?S3NNMVRrck9VZGxVUG1TRWJ2SGZ0K2tBdk0rdHhpZzZiYlk5T0grTTgyYmFY?= =?utf-8?B?M09CZGpZd1cwWHJ4K2oxRUhQcGlQOVJJZXpzcFJmOWpkUjNJbUwvSmJ3NEFs?= =?utf-8?B?NGxEbyttSm9ObDlHa0I4MVpHYkJvMFdqUmhRVEJBeUlWVVRBaTl5N2ZMdXRZ?= =?utf-8?B?U3lYK1hPNmVOdlM1SGExWGJ0U1phZkpzeHNJRytjbEg5Nys1NFBmTUp0am9F?= =?utf-8?B?R0ozM2RjNUlVd1BmZWhJRlNZQllmNGp0VjlMTkx5clpWLzVKYkYwVHp6NWsz?= =?utf-8?B?a0FDcHdudlhTZlZNa21LQkhRc25WdjBlN1g0ZWxtejBjSnIwSUFPbTJtYndD?= =?utf-8?B?TTRYS2Rac3YyV2tJQUpkY3BETEczb1MxeFNYWEZvc0lBRXQ3dy8zQmNDOVJF?= =?utf-8?B?ckNybnR2czFzZDZmdVd1akVUbVgvc1FHN2htTG41MDl2cG80cy9GVEg1TlZB?= =?utf-8?B?TXV0OEJySXJsZWNqUTZvRHN6SktiQ0NORElRSGNhcEF5bXAzZGptYjFJUzhX?= =?utf-8?Q?yHbY=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH7PR03MB7860.namprd03.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(1800799024)(366016);DIR:OUT;SFP:1101; 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> >> > } > >> > > >> > + if ( hvm && !hap && !IS_ENABLED(CONFIG_SHADOW_PAGING) ) > >> > + { > >> > + dprintk(XENLOG_INFO, "Shadow paging requested but not available\n"); > >> > >> nit: s/requested/required/, maybe? > > > > The wording matches the rest of the messages in > > arch_sanitise_domain_config(). I'm not saying that makes it correct, > > but if we word this differently we should also change the others > > IMO. > > My point is rather that HAP, or relaxed MSRs, or other settings are actively > requested via createdomain flags. Shadow is instead the consequence of not > setting HAP. You don't request shadow, you either requested something else or > you hit the error. > > It's not terrible wording, just imprecise. Hm, I see. I've always considered not requesting HAP equivalent to requesting shadow. IOW: not setting XEN_DOMCTL_CDF_hap doesn't mean "pick any possible option" but rather it's an explicit request to use shadow paging on HVM. The interface would possibly be cleaner if we had both a HAP and Shadow flags, and lack of any being selected could mean for Xen to pick the default one. Thanks, Roger.