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Tue, 29 Jun 2021 17:43:02 +0000 From: "Bae, Chang Seok" To: "Hansen, Dave" CC: "Lutomirski, Andy" , Borislav Petkov , Thomas Gleixner , Ingo Molnar , "X86 ML" , "Brown, Len" , "Liu, Jing2" , "Shankar, Ravi V" , LKML Subject: Re: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state Thread-Topic: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state Thread-Index: AQHXUAs71FpA6GLTCUWvxGMv7m3G8KsW+QQAgAAdOYCAAAnJgIAAA/+AgBRYTYA= Date: Tue, 29 Jun 2021 17:43:02 +0000 Message-ID: <3AB6DECB-2A53-4EC2-84A6-0CACE44CFC1C@intel.com> References: <20210523193259.26200-1-chang.seok.bae@intel.com> <20210523193259.26200-15-chang.seok.bae@intel.com> <872cb0a2-3659-2e6c-52a8-33f1a2f0a2cd@kernel.org> <36D0486A-D955-4C32-941A-A2A4985A450C@intel.com> <48e86785-838d-f5d4-c93c-3232b8ffd915@intel.com> In-Reply-To: <48e86785-838d-f5d4-c93c-3232b8ffd915@intel.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.120.23.2.4) authentication-results: intel.com; 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charset="us-ascii" Content-ID: <1EC7020730A7E94A8CA4EF58EB518ACB@namprd11.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: PH0PR11MB4855.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: aa3d4ed9-54e2-48f2-e097-08d93b2557e6 X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Jun 2021 17:43:02.3137 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: YjjKNMRZPTmQkTZjkt8j6fCnmoua6FXicEdhdfLkreDe3yN0gAl1yxfxtbIsODc9bB2ypKFzrVLAY1YySD4juTXVk0XDObxk6aq0w5bEtWU= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB5192 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Jun 16, 2021, at 12:01, Dave Hansen wrote: > On 6/16/21 11:47 AM, Bae, Chang Seok wrote: >> Reading XINUSE via XGETBV is cheap but not free. I don't know spending a >> hundred cycles for this WARN is big deal but this is one of the most >> performance-critical paths. > Is XGETBV(1) really a hundred cycles? That seems absurdly high for a > non-serializing register read. My apologies -- I neglect not to check the log immediately. XGETBV(1) took about 26 cycles on my test. Thanks, Chang