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:   Eric DeVolder <eric.devolder@oracle.com>
To:     linux-kernel@vger.kernel.org, david@redhat.com, osalvador@suse.de,
        corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, x86@kernel.org, bhe@redhat.com,
        ebiederm@xmission.com, kexec@lists.infradead.org
Cc:     hpa@zytor.com, gregkh@linuxfoundation.org, rafael@kernel.org,
        vgoyal@redhat.com, dyoung@redhat.com, lf32.dev@gmail.com,
        akpm@linux-foundation.org, naveen.n.rao@linux.vnet.ibm.com,
        zohar@linux.ibm.com, bhelgaas@google.com, vbabka@suse.cz,
        tiwai@suse.de, seanjc@google.com, linux@weissschuh.net,
        vschneid@redhat.com, linux-mm@kvack.org, linux-doc@vger.kernel.org,
        sourabhjain@linux.ibm.com, konrad.wilk@oracle.com,
        boris.ostrovsky@oracle.com, eric.devolder@oracle.com
Subject: [PATCH v24 10/10] x86/crash: optimize CPU changes
Date:   Wed, 28 Jun 2023 14:52:15 -0400
Message-Id: <20230628185215.40707-11-eric.devolder@oracle.com>
In-Reply-To: <20230628185215.40707-1-eric.devolder@oracle.com>
References: <20230628185215.40707-1-eric.devolder@oracle.com>
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?LJerea/3+BNz5KRRpLhJyeQrNcl095YWDm6BfQthYXVnNBdewKdI4UYKQYNo?=
 =?us-ascii?Q?lHU/r8DzdlK2iIJt0AgKfwOw1gdPswCMx0tbbXmJTNy453kv1ZRU/gXl9pIy?=
 =?us-ascii?Q?XQm1/rj9/tUDCqUllv/rzHZVYXKbobi2Hnno9RN7XVVi2+9tqYcdNE+vdcxd?=
 =?us-ascii?Q?rReTPszdDWUaXMeFOfWlvTN1wEe0jAiw+zFn76A/0vTbY2TvAAw9NOeWXCCS?=
 =?us-ascii?Q?xsu5QKN4VUeUd5mJdGBfiv0p18RBgXO1TGmawarGYQ5Q7LAmJi7wkeWUoB6O?=
 =?us-ascii?Q?5zHCzQMJMHSlNwwSepnb0oY2NfJzdAgXKKgEx6oiPwphYUaivEz+9Q4n9jIJ?=
 =?us-ascii?Q?Xt/Alrg/1T0lvcuAQsiCYvA9G+AG6szRXl6l9nqVv9nYj8eUnToMC3GDmv7L?=
 =?us-ascii?Q?0h/hgAurvcnMjv1miosIQcoTLwdUbkwP4SmFVdhF1wGrfcDqYeHYGgP9WTEZ?=
 =?us-ascii?Q?N8usykB8YdxxR0bF2u9g/kuvk3HJ6Qf1hvNfRT9ixjhZa0uh08jkV/27W8PQ?=
 =?us-ascii?Q?lIQew2D2nTCftUkIK6VWmglDCSRCeXSNI6lf5SYLASXbOtBNZ4uK2V1xaNRU?=
 =?us-ascii?Q?krlvoht8ttbZl9xQL16pk/8bkPk7jC5WiVQy+Y3IXmG2muPIaPSYKGzYff/A?=
 =?us-ascii?Q?L5zmqvyhlvcOiexd6I5HFdq8f6vUgLzSO9n9MVr0E6BGWlywFBlfRQFoJV+E?=
 =?us-ascii?Q?aR9mRzEobLqEzKD2wIWnRYuCeo2dFYZcwN5efujTGqxWjBSuKTcXOcj247xM?=
 =?us-ascii?Q?lEFo9ismBM3oSrXsoLjcfwojOHUxqCnM8utY5juJsstaXJEls7L6cUEpIFB1?=
 =?us-ascii?Q?M98CR5daikEe87QlnheNhESOZDCSRxc9kEAkSZiBso83UnyXhs1tul9LCuT1?=
 =?us-ascii?Q?PHIKYy7dD8dIpmCmWxbllOikMYJPd9tFS/WASkrKPN3vpsF9rF7bIqX4ju1U?=
 =?us-ascii?Q?bQyaEVeWUJckWeLlvayp03wML6apMZRtE+uGD2UkLJVvTMRh/0D/KWXZoiGy?=
 =?us-ascii?Q?AutKRZorGYbDJsiktq7XGTOCAiQcNPtdMwzb03UXAv6olrS+mqcT3H86CKYe?=
 =?us-ascii?Q?Yr2+SH5n51Lo2fC3kSg6FWqqqqolRJpnPShrLVVB4bowkHkhqV/oEm2IYZHJ?=
 =?us-ascii?Q?yX3CfFyoTqZ+VRwc2VpW/zlJ2mLWOcZnuDAfczL0PKGfagEyZDkfrQPVqwH+?=
 =?us-ascii?Q?nG2NwbmP5f2gMf/yoHG2zqMV5VPZ2Ez1sB0xoRFSe+JT2ri+JFTDV+AjW7s2?=
 =?us-ascii?Q?AQONiEQNF9rCMmYjXsHBIXbK8o//HmAYfLkEwWWM+sjAnXZaWbQQvVX3CSOu?=
 =?us-ascii?Q?5mJFYhMBLyo3ytB67V8OzAPY2p+4WSYGRkxPAXgNMzMbHMHblYD3M1ezukiX?=
 =?us-ascii?Q?eB/10TZEa7EzVpRdPuXzCJQjCRTPTSFQFqkGTWan3kI9NGgc2uKaBTqPre9p?=
 =?us-ascii?Q?7WgvIhZWVimEo7EgC113Ns0ScW8OftV8FJXq2HZ1Yv4JCQyoNLjhSGtdB5d2?=
 =?us-ascii?Q?fqSgZEYzHyzDlq62lbtjHMUL+e++8u5S/eQLmRVo8wWWh0pBaSUm39g8oXvU?=
 =?us-ascii?Q?KxJnJt9eTGJycz5599pfJAWm+h2EEKwH5jfc2+ZIPwVGbOv6wOUXzF0LCtQU?=
 =?us-ascii?Q?Ow=3D=3D?=
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: =?us-ascii?Q?TkAVws5gkeoJAKPfhXE8dxZ5cgc0+GzLdUg8jPovMCw3+U7/BfDv84kmEUpy?=
 =?us-ascii?Q?RmYPRNUcizc4T05koyMO4J16dKTlH6Coq1ajlb1QXcB8XKW33MzJA8GotGPr?=
 =?us-ascii?Q?/yPpq2lX7Uh1B/7ChYCtRjKsA2hGG1zzQplIj3cjdGTGEAepgPyuyKFs7n0f?=
 =?us-ascii?Q?vDhdGGN6j4RaoCubEBspwz3w2QShB7ao7q36hk8TNj5awfr3oeK5z81soDVz?=
 =?us-ascii?Q?Db/RYaY4W4Shi/wGL1JwriW63cI36Lb+3FTG2vI0prv00H/xBQI0Jh+uOlXD?=
 =?us-ascii?Q?a++nxRLxqcpp7stlzXI0QJKfmg/cwvvDQRcSs86E4cEiuOQQ+CKzE4USPq8M?=
 =?us-ascii?Q?v6xc9I1ZVzvCajomqKXUYMcfooK+OES9WfwOIhmQ40f0qMSqSM+RMfiOFnqr?=
 =?us-ascii?Q?A3TPNDTB2pYhH/zkMGJppRbE63nJG0pwysiuNTcJ/9HTSpYVbELcvpn0JtRm?=
 =?us-ascii?Q?FSgF8Kb35ylOLtGNVozPhjf7b/TENnRqfB3jq5RcRLIU5jBCXVhAiTq10b5Z?=
 =?us-ascii?Q?LKBJUU5BIW7m1pxo3LA1QsggttoRJLoJ+SKUrwtxyJzV/dTfjNJlirXEF992?=
 =?us-ascii?Q?ejby+4mTqUykB2ecebcC2ZMF7aVmybobPRnxFMnbpML/LJOhwmc71Lr11PyO?=
 =?us-ascii?Q?gxPqPY+Jl3VUwikchfsSqZrHo25VAJoSsF5YgQUenWmilDyP8pv0gNJCp4pe?=
 =?us-ascii?Q?mLELbr73/ZG5OQEtQ47ukcHiKgg0v29ZSgtI8rgdz7HLZQsnMbKwRcKvqtRu?=
 =?us-ascii?Q?BWebzxTKIRF/2tyOHKhOyouJ/yHrQWigARJbyoavS8q3b3+MoxsT/Khe3HqE?=
 =?us-ascii?Q?tRbqfyspmfrPASl2/sBTlNLwWUd0uxRyeF7W0RbiUPBehinf98PYtUw5p/2C?=
 =?us-ascii?Q?JlgqAFiBago9S4jGBdzYDlVw+ViyPbeu2nj3LEcOSwFK5H7mi7rc8vtUES0p?=
 =?us-ascii?Q?PVFDoiq94WP/z7bEG5Nh0jtGJRXTHJRGgM4iPKSYOVvEoOF+oL4vQ8uZiFrp?=
 =?us-ascii?Q?cU5YVUxlVIjcfDAMZ/v+eSfhSiZCgbRM28utGkuRtxB32DcwJUqytLEXyP8f?=
 =?us-ascii?Q?y0DtaUPECkWHJQMUa2oRRXa5vpOb8mU8hdx7zbM0qdSg6Nc5xiyvBKBIBbtz?=
 =?us-ascii?Q?4tzTFtOauBus16z/tv0t0B4joIZ89ZNz/WIVUaoftAeFysdI16609Rpqfxac?=
 =?us-ascii?Q?uaOju03BW4fiv+8UD7MdytFhMC7QqUTknnZiOT5gxJm1J6NfCq3jqXTpSqCq?=
 =?us-ascii?Q?wfV6F0GV6AKrAImXUlzqbmtFC/4+XUT8rKJQhaAmAxw3+hKtgbh4cdzFB5tD?=
 =?us-ascii?Q?a+QvHf6ewQjUEBo6C4bqX1kQBFGRGvD80LA9z4pcwCs3fCWlPkqFX/jhpKEi?=
 =?us-ascii?Q?91rhTs7bDDBps4K0rUthlUgXCbU1INXyjRRIyKhUfaWBh/cgTcgoXlIxgwx9?=
 =?us-ascii?Q?7QM9ayw6caI=3D?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: e85c2bcc-b5f7-4902-dde9-08db7808e13a
X-MS-Exchange-CrossTenant-AuthSource: CO1PR10MB4531.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jun 2023 18:52:53.8648
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: Xku8gPtmRl+UAboMmG/ZI+rtftAEaLZh0FeeV7K48K0IsrWZKdgHSSqpxC0p7B+Tz9qG7nZDAuJeM2Zel+NdTmzzawT1nkMdiqlHGTQeD/o=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV3PR10MB7820
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.591,FMLib:17.11.176.26
 definitions=2023-06-28_13,2023-06-27_01,2023-05-22_02
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 malwarescore=0 mlxscore=0
 mlxlogscore=999 bulkscore=0 spamscore=0 phishscore=0 suspectscore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2305260000
 definitions=main-2306280168
X-Proofpoint-GUID: YeSnm4XcdNd5j4J4e_3Dd3VpNl7vUEaY
X-Proofpoint-ORIG-GUID: YeSnm4XcdNd5j4J4e_3Dd3VpNl7vUEaY
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

crash_prepare_elf64_headers() writes into the elfcorehdr an ELF
PT_NOTE for all possible CPUs. As such, subsequent changes to CPUs
(ie. hot un/plug, online/offline) do not need to rewrite the elfcorehdr.

The kimage->file_mode term covers kdump images loaded via the
kexec_file_load() syscall. Since crash_prepare_elf64_headers()
wrote the initial elfcorehdr, no update to the elfcorehdr is
needed for CPU changes.

The kimage->elfcorehdr_updated term covers kdump images loaded via
the kexec_load() syscall. At least one memory or CPU change must occur
to cause crash_prepare_elf64_headers() to rewrite the elfcorehdr.
Afterwards, no update to the elfcorehdr is needed for CPU changes.

This code is intentionally *NOT* hoisted into
crash_handle_hotplug_event() as it would prevent the arch-specific
handler from running for CPU changes. This would break PPC, for
example, which needs to update other information besides the
elfcorehdr, on CPU changes.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Acked-by: Hari Bathini <hbathini@linux.ibm.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 arch/x86/kernel/crash.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index caf22bcb61af..18d2a18d1073 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -467,6 +467,16 @@ void arch_crash_handle_hotplug_event(struct kimage *image)
 	unsigned long mem, memsz;
 	unsigned long elfsz = 0;
 
+	/*
+	 * As crash_prepare_elf64_headers() has already described all
+	 * possible CPUs, there is no need to update the elfcorehdr
+	 * for additional CPU changes.
+	 */
+	if ((image->file_mode || image->elfcorehdr_updated) &&
+		((image->hp_action == KEXEC_CRASH_HP_ADD_CPU) ||
+		(image->hp_action == KEXEC_CRASH_HP_REMOVE_CPU)))
+		return;
+
 	/*
 	 * Create the new elfcorehdr reflecting the changes to CPU and/or
 	 * memory resources.
-- 
2.31.1