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Message-ID: <6c8fd8b4-85ed-6599-5761-a3f6e9fdeb36@suse.com> Date: Mon, 15 Aug 2022 10:26:52 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH] x86/spec-ctrl: Use IST RSB protection for !SVM systems Content-Language: en-US To: Andrew Cooper Cc: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Wei Liu , Xen-devel References: <20220805103814.23032-1-andrew.cooper3@citrix.com> From: Jan Beulich In-Reply-To: <20220805103814.23032-1-andrew.cooper3@citrix.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR0P281CA0013.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:15::18) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 5b70ad77-0e72-4b9b-8c4c-08da7e97e8a5 X-MS-TrafficTypeDiagnostic: HE1PR0401MB2634:EE_ X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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> > + /* > + * For SVM, Xen's RSB safety actions are performed before STGI, so > + * behave atomically with respect to IST sources. > + * > + * For VT-x, NMIs are atomic with VMExit (the NMI gets queued but not > + * delivered) whereas other IST sources are not atomic. Specifically, > + * #MC can hit ahead the RSB safety action in the vmexit path. > + * > + * Therefore, it is necessary for the IST logic to protect Xen against > + * possible rogue RSB speculation. > + */ > + if ( !cpu_has_svm ) > + default_spec_ctrl_flags |= SCF_ist_rsb; Only now, when I'm about to backport this, it occurs to me to ask: Why is this !cpu_has_svm rather than cpu_has_vmx? Plus shouldn't this further be gated upon HVM actually being in use (i.e. in particular CONFIG_HVM=y in the first place)? Jan