Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   "Elliott, Robert (Servers)" <elliott@hpe.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>
CC:     "davem@davemloft.net" <davem@davemloft.net>,
        "tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>,
        "ap420073@gmail.com" <ap420073@gmail.com>,
        "ardb@kernel.org" <ardb@kernel.org>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2 05/19] crypto: x86/crc - limit FPU preemption
Thread-Topic: [PATCH v2 05/19] crypto: x86/crc - limit FPU preemption
Thread-Index: AQHY3oYIGawv1P27002drIVzPEZ09a4LkfsAgAFVjQA=
Date:   Thu, 13 Oct 2022 22:34:02 +0000
Message-ID: <MW5PR84MB1842FCF31D9CE954873250BCAB259@MW5PR84MB1842.NAMPRD84.PROD.OUTLOOK.COM>
References: <20221006223151.22159-1-elliott@hpe.com>
 <20221012215931.3896-1-elliott@hpe.com>
 <20221012215931.3896-6-elliott@hpe.com>
 <Y0dxJrRx/Neo4r1Z@gondor.apana.org.au>
In-Reply-To: <Y0dxJrRx/Neo4r1Z@gondor.apana.org.au>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?SYnPMpT3tqtbqvhHKki55RbxtkzvJLVlGCh/lrx64J3H7HxPRSAqW39VOYVE?=
 =?us-ascii?Q?D9NynV6psrfa15SrGyw1oHRL5sUrMSOmxPVud8NIqVaf6YVJ9OP9ciLSVa+i?=
 =?us-ascii?Q?i9fxMgWeLJcvE/te9/6Dp35XkJPMJ+lzOGKg5bH5qHN/FuK7eLgcJhhZNZNF?=
 =?us-ascii?Q?gW/rdKg8ty2q8C8+da4R+BN6luVct9pm/lptYAYEHKZrKoyIxBavRUVC3OUO?=
 =?us-ascii?Q?nQvvMJGaMaXJPuikP6KLXr3udYcKjgz0Lq9SQ7nE+sXQ2DNMMRa4GDpDlXSh?=
 =?us-ascii?Q?BNhvqkAtQo+pr6td2HY7J21Y4ZEhsHOVd/ewiD9k8Ijt+pHXKuYtBJJ62K/t?=
 =?us-ascii?Q?03YICj0gTHjI5eUDMG32IAm/AGGudvo9wlcVFO4CK1O82/Xt9Cfjhg5LIQYA?=
 =?us-ascii?Q?a0JXXGQBWDZh9c6x6lHsxNYKVqO9RbzwJolPvkCbbjwLfvNJ1Wo88tgEvRys?=
 =?us-ascii?Q?vVRh+/4Uhl0hHrheEKoUYdHrdTS6IUI5KZRS7OmvN2YsU0Z/6wdIFW4+ZWho?=
 =?us-ascii?Q?4GTA/caqNIIjqN1d32sYCbjJKadSeFPYL98iDTcQTp41FRaLvFPcOahsPg1H?=
 =?us-ascii?Q?epM91XXjZEGSaCwwwJqiH1Y5Ks9R4Zt8azzpZYgHCDedZDLIBz5JRjfbaLk3?=
 =?us-ascii?Q?5nONRh+4Bj5dNkBMk1yM6nYR3Ym+BdIIVXVimk+OziM1qHsSb3Di4YBV9KKr?=
 =?us-ascii?Q?lHPieWxbV6T+WSkEBPKo8mTDr+DI7b5FuCsNIg8xtVM+ojc2W9pTUd6Qbq9s?=
 =?us-ascii?Q?NpQ8ux7QUHqPdtufVU4/0z9MAFAwz56iVsxXMNhRdzGHQchEi1BrZb+Cc6FD?=
 =?us-ascii?Q?+DYNZRgE0YfYeueHbsWclxxvvTTazcx+IPVM8TLsJ16djab+JG7Qbe4rDzsB?=
 =?us-ascii?Q?DYsfq0Fkr5AQIRyFZ4cbA6rwKWW/S5pY8v+0XjlXhJwLV7ZZEy/z/l7n0HIH?=
 =?us-ascii?Q?sF8zf6o53MeDzxjgz5/4L8dZC/NKDtEjHRt+1jYcMFb6fOUKLZ3dkUUliag0?=
 =?us-ascii?Q?lviACvmro/6hEmfu8eHDzEVp4fAUDT3cJ+kzFw32s5zC+hQIJnKJs0wuboBt?=
 =?us-ascii?Q?0N74h+v0R2WOy3Ie4Ks7cueIJD4Ih/c98xHYryUJApq5FdB1/QOhH/i8jfMP?=
 =?us-ascii?Q?ChAqDvR1mM+Qcbxok/BKzczgc9qSDg03BbxIk9SQSj2uwIGR7RvMnV48CYPJ?=
 =?us-ascii?Q?1ay4C4eMxQRsNAiepLq+ihT+j1YxXf9hXN82QYeDb0FiEUoD5VNWcb9H785d?=
 =?us-ascii?Q?0fZIxkboraoQd+UBOVqWWyxMFZnf8POym+XxyWstaWglpI0v4KMJcmwevyG5?=
 =?us-ascii?Q?3k7z71k/Iss3Zqxa8nNbzo5nxtYbm7IrE8yeyLi0/V/uAxp2l1ch3hUCP/up?=
 =?us-ascii?Q?tF4ygN9M3Y0iVWQjWtzskAEfyUM8ETtGHDGuRcEIQewoomO5hx5e1kFZRcK8?=
 =?us-ascii?Q?Vghu/rfLGT6qu2/EL4XshbfaM0PXOLbgTanR5V+sPqmXEVDviUFni/LegY82?=
 =?us-ascii?Q?zLIW7ObsSGOQzRiKqPfHPfXFEn/G6N4lJQuryzsawiyqWERNRzmv0fH6Vjkf?=
 =?us-ascii?Q?rFBNciz9qIDrwGst2FY=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: MW5PR84MB1842.NAMPRD84.PROD.OUTLOOK.COM
X-MS-Exchange-CrossTenant-Network-Message-Id: 1acd0ecf-0bd6-4b79-40a6-08daad6b078d
X-MS-Exchange-CrossTenant-originalarrivaltime: 13 Oct 2022 22:34:02.5681
 (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: cpKVHCTS+RNtLWM7FVVDtGe5XNfxin2FvU8CMTDgMiAyzBFsGuyEvqoe2S+3iM/Y
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR84MB1422
X-OriginatorOrg: hpe.com
X-Proofpoint-ORIG-GUID: Wy9YLNyCqFeNKU1TZiR2nNe7j_oRVPDc
X-Proofpoint-GUID: Wy9YLNyCqFeNKU1TZiR2nNe7j_oRVPDc
X-HPE-SCL: -1
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1
 definitions=2022-10-13_08,2022-10-13_01,2022-06-22_01
X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 malwarescore=0
 suspectscore=0 priorityscore=1501 impostorscore=0 mlxlogscore=869
 phishscore=0 spamscore=0 lowpriorityscore=0 mlxscore=0 adultscore=0
 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2209130000 definitions=main-2210130125
X-Spam-Status: No, score=-2.8 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 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-crypto.vger.kernel.org>
X-Mailing-List: linux-crypto@vger.kernel.org


> -----Original Message-----
> From: Herbert Xu <herbert@gondor.apana.org.au>
> Sent: Wednesday, October 12, 2022 9:00 PM
> To: Elliott, Robert (Servers) <elliott@hpe.com>
> Cc: davem@davemloft.net; tim.c.chen@linux.intel.com; ap420073@gmail.com;
> ardb@kernel.org; linux-crypto@vger.kernel.org; linux-kernel@vger.kernel.o=
rg
> Subject: Re: [PATCH v2 05/19] crypto: x86/crc - limit FPU preemption
>=20
> On Wed, Oct 12, 2022 at 04:59:17PM -0500, Robert Elliott wrote:
> >
> > @@ -170,9 +179,17 @@ static int __crc32c_pcl_intel_finup(u32 *crcp, con=
st u8
> *data, unsigned int len,
> >  				u8 *out)
> >  {
> >  	if (len >=3D CRC32C_PCL_BREAKEVEN && crypto_simd_usable()) {
> > -		kernel_fpu_begin();
> > -		*(__le32 *)out =3D ~cpu_to_le32(crc_pcl(data, len, *crcp));
> > -		kernel_fpu_end();
> > +		do {
> > +			unsigned int chunk =3D min(len, FPU_BYTES);
> > +
> > +			kernel_fpu_begin();
> > +			*crcp =3D crc_pcl(data, chunk, *crcp);
>=20
> How about storing the intermediate result in a local variable
> instead of overwriting *crcp?
>=20
> Thanks,

The _update function does so, and it's not marked const here,
so seemed prudent to keep up to date.

Do the callers understand it's no longer valid after finup, or
is there any case they might treat finup like an update and try
again?