Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   "Hawkins, Nick" <nick.hawkins@hpe.com>
To:     Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>
CC:     "Verdun, Jean-Marie" <verdun@hpe.com>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Mark Rutland <mark.rutland@arm.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Joel Stanley <joel@jms.id.au>
Subject: RE: [PATCH v1] ARM: A9: Add ARM ERRATA 764319 workaround
Thread-Topic: [PATCH v1] ARM: A9: Add ARM ERRATA 764319 workaround
Thread-Index: AQHYYX9/lEqShxGKek6V2FmsHnxQM60XuXoAgABMyYCAABLbAIAAE4wAgADBDEA=
Date:   Wed, 11 May 2022 12:23:57 +0000
Message-ID: <PH0PR84MB171830414ADC0DD69BD4116788C89@PH0PR84MB1718.NAMPRD84.PROD.OUTLOOK.COM>
References: <20220506192957.24889-1-nick.hawkins@hpe.com>
 <CAK8P3a045Di_zRomezeah0ZoSGPw0Z6YoYkZtoxx1qOXAtKbbw@mail.gmail.com>
 <7C103AEB-3111-4AE6-9645-CF590388A879@hpe.com>
 <CAK8P3a0OS+4XTG9VmfPwbuQoT+_G5-fSatbJ0g8Y7Y+O6-3YLQ@mail.gmail.com>
 <20220510141124.GB28104@willie-the-truck>
In-Reply-To: <20220510141124.GB28104@willie-the-truck>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?jHMkdc/l4HpzmB16tgvjBmimb37xYTOaMba/yoNhq3q6zMrmr+ZZN0FLAx9c?=
 =?us-ascii?Q?fq26ysXZ7kYu6APGK9F7daxueVap1ncMJt9zkGE5A8OTjt0Hrh3mEWSQDFYk?=
 =?us-ascii?Q?ZU8tM3SM10p9/XuF/5UK955BR+BTbKG0IKN5hBP8HNvOV/YDQ9hy8He2js0u?=
 =?us-ascii?Q?dnObz5fmlC3uX+fk5MwD5WJrKk7htAm+PLmoWBqWvGfOoY6U0+mbM4q53NUE?=
 =?us-ascii?Q?kg9YwiHNgpddueotgsb96eLLs4UICfRQ6PPkVLhI51vKr7bXed2jJMTqa8uA?=
 =?us-ascii?Q?AgJf9ic1Wsk5MlwNw/oe30XlXJTileEpCBX+IHo88r78vaWKKSp/iZGrxVQM?=
 =?us-ascii?Q?GAw/JupJG1nV8nP8KQlZUywx+eOfeWkDeEv8D3zQ5tvYtZ0d+JW9XVSsic0D?=
 =?us-ascii?Q?WpHFbJ+QhF/TL8p83ZTPCkkkfYeeYlDZQFmn+57SUX7nNy3Ikum80UWa7Vwj?=
 =?us-ascii?Q?gzy4EmEj5QF6+jJg5smpzN8Cq2FirAJyrZrOuaSzupI+/BhENP/nkbpmMvGi?=
 =?us-ascii?Q?o3aMm4fJWc8RlzHpelMflkWAgLE1lBE391CnXIgaGvjHMSSVmQltbeLIUJSr?=
 =?us-ascii?Q?xpS9TQlkgHe0YdNF97GkUfzaYQ7fWVuYC4Fgqs65JCJUuPE6iNGQ1i7RoDCQ?=
 =?us-ascii?Q?EX8x5NxfdQx7zH4tR+jV5zJvpLWf84Ti/6VPqdc89YZziDRK8r+D3pXSbRQp?=
 =?us-ascii?Q?t3T+aeq6hJi36BfRc4rZN+EIBJpvIteM92mAQ56Wb4hmieGyLOcGlBjFcn5H?=
 =?us-ascii?Q?3eEVAT4IEUtTf1310LErUVaCsletpbhZRXL6SK2VTe3ZxkpmxSzz1fdcDL6O?=
 =?us-ascii?Q?6CYzXzcjCy+olQaqgk32z9MiZbYHRYqxBNQY6yy2RSPXVa8Uo1X7/ChKFOyG?=
 =?us-ascii?Q?XuwXulfYK6D/Ga53WiBh2a8RotHYIywiPuFsM7GFDyLXXWm14hUn4mgm2uXh?=
 =?us-ascii?Q?vMzc82XLDlUof1mneNltaZNy8gwofrLwwYNjiooh2l7UjLlpWdmG9vSmuElk?=
 =?us-ascii?Q?OYOyA9G8C8bvscLkSK/xeMMdT6azyUZUt4ketowo1nEHBxdm/xcffmR3URNi?=
 =?us-ascii?Q?ECoaRcWohdq/xorRVG41CzaUtvE71f7vmoKfC1Gu5cZpg29L835LHTm+NNAo?=
 =?us-ascii?Q?8+e00Sdym8deXZKGwjFUYxff1OEV4n5+mI2ZpdMrYMfiT3hO4E/w1aqv0HIR?=
 =?us-ascii?Q?980yqguqUuxBUPOl9oz8+eRcE2j1ScsMJ8xYcOG1XzzTlhepCUmOkcWzxKmm?=
 =?us-ascii?Q?IT5vyWhs1ZJIOOXFTNZyTpKXV3tI+ZunQFjKVtHEzuE3CNU8ZWeB7rkGeR72?=
 =?us-ascii?Q?GJ3mJjOHyCGzkZt/HGTfi+Den2YkMN0TRGNs7c5LusKb+pxlzpwr8lBjtlOF?=
 =?us-ascii?Q?b8RaOobR6OjutkK3GL5k+5WwXpkj5+fnlg/7PoRi70Qt72G1heMTmsb4nAj4?=
 =?us-ascii?Q?Dy/g930dayoVlfET+G+GwxiutqXEDlu4jfJsM9eu70pQzIkSZOeC3ry9DCGK?=
 =?us-ascii?Q?z75hZ4SJbpb4Xap1vkKKfwLhdZ2D94//hBQZweiGRariR0kBCqCRZHrS1ryM?=
 =?us-ascii?Q?ue43oXo8ZQj0AfW21lePckfd0mXs7TIz3O6KZOu3cKaWwLAojHYK4w2Hc86B?=
 =?us-ascii?Q?YVNjVITcAIC9jWs3ZAcUppxdx9vPepeQGfCWZ9lkb4c3rV8gih6kbaBlZIuW?=
 =?us-ascii?Q?W/SoxjlkHDMSyZlvHTHWq4Y+fLNoGmOL4flw7Xjrw48saeQmKiV6qf+fP5MA?=
 =?us-ascii?Q?nQPpF+wCQw=3D=3D?=
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-AuthSource: PH0PR84MB1718.NAMPRD84.PROD.OUTLOOK.COM
X-MS-Exchange-CrossTenant-Network-Message-Id: 7017f1e8-23a5-42e4-2974-08da33491f75
X-MS-Exchange-CrossTenant-originalarrivaltime: 11 May 2022 12:23:57.9123
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 105b2061-b669-4b31-92ac-24d304d195dc
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: sZir2iRD18CtQ+Fb5eZSP3IbUFqVpA4QVoirStLol/H99IHJNojnXh/RxW6WsFw3QVRMip837cdcB3UPhyK0Vw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR84MB1720
X-OriginatorOrg: hpe.com
X-Proofpoint-GUID: KZs8ToWric66CRe6IQAWPcBvsTqL-MIm
X-Proofpoint-ORIG-GUID: KZs8ToWric66CRe6IQAWPcBvsTqL-MIm
X-HPE-SCL: -1
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.205,Aquarius:18.0.858,Hydra:6.0.486,FMLib:17.11.64.514
 definitions=2022-05-11_03,2022-05-11_01,2022-02-23_01
X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 adultscore=0
 priorityscore=1501 suspectscore=0 mlxlogscore=900 phishscore=0 bulkscore=0
 mlxscore=0 clxscore=1015 malwarescore=0 lowpriorityscore=0 spamscore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000
 definitions=main-2205110057
X-Spam-Status: No, score=-3.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,
        SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED
        autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, May 10, 2022 at 03:01:26PM +0200, Arnd Bergmann wrote:
> > On Tue, May 10, 2022 at 1:53 PM Verdun, Jean-Marie <verdun@hpe.com> wro=
te:
> > >
> > > Hi Arnd,
> > >
> > > >    Hi Nick,
> > >
> > > >    This seems a bit more complex than necessary. Can't you just use=
 a custom
> > > >    inline asm with an ex_table entry to catch the fault? Have a loo=
k at
> > > >    __get_user_asm() for an example.
> > > >
> > > >           Arnd
> > >
> > > We got inspired from debug_reg_hook within the same source file (=20
> > >./arch/arm/kernel/hw_breakpoint.c ). We chose that path to keep=20
> > >coherency  within the source code. We can implement the same fix by=20
> > >using an ex_table  entry, but this will create two different ways at=20
> > >catching unknown instruction  within the same source file. Will that b=
e ok ?
> >=20
> > I got a little lost trying to find where the breakpoint instruction=20
> > comes from that gets trapped here, but I would guess that they had to=20
> > do this using an undef_hook because the ex_table approach does not=20
> > work there for some reason.
> >=20
> > I would still pick the ex_table method here if that works.

> IIRC, the ex_table handlers are called only for data aborts and are inten=
ded to be used to handle cases where we take a fault on a memory access (e.=
g.
translation fault). In this case, we're taking an undefined instruction exc=
eption on a cp14 access and so the undef_hook is the right thing to use.

Hello Arnd,

Given Will's input would you like me to still use the ex_table method?

Thanks,

-Nick Hawkins