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Date: Mon, 20 Oct 2025 09:44:29 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Demi Marie Obenour Cc: Alejandro Vallejo , Jan Beulich , Grygorii Strashko , Sergiy Kibrik , Andrew Cooper , Paul Durrant , "xen-devel@lists.xenproject.org" Subject: Re: [PATCH v5] x86: make Viridian support optional Message-ID: References: <20250930125215.1087214-1-grygorii_strashko@epam.com> <3e4e4bc5-aa47-4357-9327-df2a9b9c9a1b@suse.com> <9248eda6-cf9b-4fdf-ab32-66e777585f65@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: LO4P123CA0411.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:189::20) To DM6PR03MB5227.namprd03.prod.outlook.com (2603:10b6:5:247::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR03MB5227:EE_|BN8PR03MB5105:EE_ X-MS-Office365-Filtering-Correlation-Id: fe781176-a31b-4e08-90ce-08de0fb4e3f3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016; 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This is to improve performance and compatibility of Windows VMs. > >>>> > >>>> What is "paravirtualized I/O" about in this context? > >>> > >>> Hypervisor-assisted IPIs, TLB flushes, etc. Or so I understood back when I said > >>> that looked ok. I see there could be confusion with Xen PV device protocols, > >>> but as far as the user of the help message is concerned it makes no difference. > >>> > >>> One could even remove the examples and leave it as "... for Hyper-V guests. This > >>> is to...". They are truly inconsequential. > >>> > >>> All that matters is that (modern) Windows won't run without it, and that it > >>> provides some indeterminate hypervisor-provided assists to try to reduce some > >>> virtualization overheads. > >> > >> Qubes OS doesn't expose Viridian at all, which is why it wasn't > >> vulnerable to XSA-472. It still runs Windows guests just fine. > > > > Can you run Windows 11? > > I haven't tried it, but it is documented as working. > > > I don't remember which, but I do know some versions of Windows refuse to boot > > if they determine they are virtualised and don't see the mandatory parts of > > the TLFS. > > > > If 11 works, maybe Windows Server? > > Windows Server is more likely. FTR, for unrelated reasons I've tested Windows Server 2025 without Viridian, and it does work, albeit painfully slow. Regards, Roger.