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Mon, 29 Mar 2021 18:14:48 +0000 From: "Bae, Chang Seok" To: Jann Horn CC: Borislav Petkov , Andy Lutomirski , "Thomas Gleixner" , Ingo Molnar , "the arch/x86 maintainers" , "Brown, Len" , "Hansen, Dave" , "Liu, Jing2" , "Shankar, Ravi V" , kernel list Subject: Re: [PATCH v4 14/22] x86/fpu/xstate: Expand the xstate buffer on the first use of dynamic user state Thread-Topic: [PATCH v4 14/22] x86/fpu/xstate: Expand the xstate buffer on the first use of dynamic user state Thread-Index: AQHXCIQDYHRUMzQ+BU6HvOsZgq/N2KqWqq4AgATTFgA= Date: Mon, 29 Mar 2021 18:14:48 +0000 Message-ID: <138A0E3D-4794-43C7-861A-4011534A09A8@intel.com> References: <20210221185637.19281-1-chang.seok.bae@intel.com> <20210221185637.19281-15-chang.seok.bae@intel.com> In-Reply-To: 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: google.com; dkim=none (message not signed) header.d=none;google.com; dmarc=none action=none header.from=intel.com; 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charset="us-ascii" Content-ID: <9534083BFD53A74A96B1FC19D61B170F@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: 2a2c0f68-271b-4c3d-6a88-08d8f2de89ce X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Mar 2021 18:14:48.0258 (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: tuSLFs/JqIwGDQlMYN+mbTnbhNX0FyxC2mIKP8ta96UpItP+BEe0mDIS+ImiX0KN5FYz/sAVZJnAoa5sb7NG/AJRu1LVOmgVvLp6o4OC6/U= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB5079 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mar 26, 2021, at 09:34, Jann Horn wrote: > On Sun, Feb 21, 2021 at 7:56 PM Chang S. Bae w= rote: >>=20 >> + if (handle_xfirstuse_event(¤t->thread.fpu)) >> + return; >=20 > What happens if handle_xfirstuse_event() fails because vmalloc() > failed in alloc_xstate_buffer()? I think that should probably kill the > task with something like force_sig() - but as far as I can tell, at > the moment, it will instead end up at die(), which should only be used > for kernel bugs. This question was raised on v1 before [1]. In the end, people suggested to handle the failure, e.g., with tracepoints = or stats. So, proposed this on the allocation site: + state_ptr =3D vmalloc(newsz); + if (!state_ptr) { + trace_x86_fpu_xstate_alloc_failed(fpu); + return -ENOMEM; + } Also, I tried to justify this to Boris [2]: >> Maybe it is possible to backtrack this allocation failure out of #NM >> handling. But the tracepoint can provide a clear context, although lim= ited >> to those using it. > Yes, add it when it is really needed. Not slapping it proactively and > hoping for any potential usage. Let me know if you have a better way. Thanks, Chang [1] https://lore.kernel.org/lkml/c4669d5f-11b8-3879-562c-78a791b86229@intel= .com/ [2] https://lore.kernel.org/lkml/20210204131002.GA17068@zn.tnic/