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Message-ID: <7d41940f-e671-954c-1afc-510e4fa674fa@suse.com> Date: Wed, 10 May 2023 10:15:31 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.10.1 Subject: Re: [PATCH 3/3] x86: Use CpuidUserDis if an AMD HVM guest toggles CPUID faulting Content-Language: en-US To: Andrew Cooper , Alejandro Vallejo Cc: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Wei Liu , Xen-devel References: <20230505175705.18098-1-alejandro.vallejo@cloud.com> <20230505175705.18098-4-alejandro.vallejo@cloud.com> From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR2P281CA0130.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:9e::11) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|AS8PR04MB7672:EE_ X-MS-Office365-Filtering-Correlation-Id: 4b309d85-d4c6-4cd9-ab87-08db512eba31 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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If they try to modify the Intel MSR that enables >>> the feature, trigger levelling so AMD's version of it (CpuidUserDis) >>> is used instead. >>> >>> Signed-off-by: Alejandro Vallejo >>> --- >>> xen/arch/x86/msr.c | 9 ++++++++- >>> 1 file changed, 8 insertions(+), 1 deletion(-) >> Don't you also need to update cpu-policy.c:calculate_host_policy() >> for the guest to actually know it can use the functionality? Which >> in turn would appear to require some form of adjustment to >> lib/x86/policy.c:x86_cpu_policies_are_compatible(). > > I asked Alejandro to do it like this. > > Advertising this to guests requires plumbing another MSR into the > infrastructure which isn't quite set up properly let, and is in flux > from my work. Maybe there was some misunderstanding here, as I realize only now. I wasn't asking to expose the AMD feature, but instead I was after /* 0x000000ce MSR_INTEL_PLATFORM_INFO */ /* probe_cpuid_faulting() sanity checks presence of MISC_FEATURES_ENABLES */ p->platform_info.cpuid_faulting = cpu_has_cpuid_faulting; wanting to be extended by "|| boot_cpu_has(X86_FEATURE_CPUID_USER_DIS)". That, afaict, has no connection to plumbing yet another MSR. Jan