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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BN9PR11MB5276.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 1cb4fdcf-7659-48c5-7bfd-08d9d0aea7b2 X-MS-Exchange-CrossTenant-originalarrivaltime: 06 Jan 2022 00:51:20.3705 (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: Ry1JePrRt/M5C3zh4qo4xI5XC+EkotlVAE72ey9k5IPQ+Pd0WARTFDEkdztiYnICgbpfzAc54GL85fIMoJLZuQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN9PR11MB5275 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Paolo Bonzini > Sent: Wednesday, January 5, 2022 9:07 PM >=20 > On 1/5/22 13:35, Yang Zhong wrote: > > +int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 > xfeatures) > > +{ > > + lockdep_assert_preemption_enabled(); > > + >=20 > The old fpu_update_guest_perm_features(guest_fpu) is equivalent to >=20 > fpu_enable_guest_xfd_features(guest_fpu, guest_fpu->perm); >=20 > Missing doc comment: >=20 > /* > * fpu_enable_guest_xfd_features - Enable xfeatures according to guest > perm > * @guest_fpu: Pointer to the guest FPU container > * @xfeatures: Features requested by guest CPUID > * > * Enable all dynamic xfeatures according to guest perm and requested > CPUID. > * Invoked if the caller wants to conservatively expand fpstate buffer i= nstead > * of waiting until XCR0 or XFD MSR is written. > * > * Return: 0 on success, error code otherwise > */ It's not equivalent. The old interface enables all xfeatures allowed by guest perm while the new one just enables feature bits according to the caller request. It also becomes a more general interface instead of being only for conservative expansion. Since both points in the old comment don't hold now and this function is obvious, we didn't put a comment here (on par with other KVM helpers in that block). If still necessary we could add one like below: /* * fpu_enable_guest_xfd_features - Enable xfeatures for guest fpu containe= r * @guest_fpu: Pointer to the guest FPU container * @xfeatures: Features requested by the caller * * Enable dynamic xfeatures and expand guest fpstate buffer accordingly. * KVM should call this function before the requested xfeatures are used * by the guest. * * Return: 0 on success, error code otherwise */ >=20 > Also, the check for 32-bit is slightly imprecise: >=20 > /* Dynamic xfeatures are not supported with 32-bit kernels. */ > if (!IS_ENABLED(CONFIG_X86_64)) > - return 0; > + return -EINVAL; >=20 > since we only get here with xfeatures !=3D 0 (if it compiles, just removi= ng > the IS_ENABLED check altogether would be even better). With these change= s, >=20 > Reviewed-by: Paolo Bonzini >=20 > Thanks, >=20 > Paolo