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;
Message-ID: <bc5ec4a0-a33c-1ca1-c66d-635f4e0b9731@oracle.com>
Date:   Fri, 1 Apr 2022 13:35:28 -0500
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.3.1
Subject: Re: [PATCH v5 8/8] x86/crash: Add x86 crash hotplug support for
 kexec_load
Content-Language: en-US
To:     Baoquan He <bhe@redhat.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, vgoyal@redhat.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com,
        robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com,
        konrad.wilk@oracle.com, boris.ostrovsky@oracle.com
References: <20220303162725.49640-1-eric.devolder@oracle.com>
 <20220303162725.49640-9-eric.devolder@oracle.com>
 <YkWMFzxJpkiTjKvL@MiWiFi-R3L-srv>
From:   Eric DeVolder <eric.devolder@oracle.com>
In-Reply-To: <YkWMFzxJpkiTjKvL@MiWiFi-R3L-srv>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?SkRWQmwzSW13T0VabVJXTldyS3J2WXltMGlPTmxBc0tUeVpJbW9MTVd4a1Fn?=
 =?utf-8?B?R0w0VXEvcFZJUTFCRjRBRUNidmQ3eHdwRjhUVUN5V3hnZU1yVDBBaFR1bGU5?=
 =?utf-8?B?dDgwUlg4bFozRERuei9HdGFjdXFsdUc4N0M3Vml0aVVJR3hsNUFHODZGd1M0?=
 =?utf-8?B?RFl0eldzUjROd0NoSGEzMzl4ZmxZaFp5TTFlckt0TnBpd2JzZDVSWHhDbHBM?=
 =?utf-8?B?a2lGQXNjbk9nU09nSXJrMVEyaVB3bzFDM1pIdnZsQlR4MjNXZ3Q5ZFNSWUpL?=
 =?utf-8?B?b0loeFdrd2MvUU1aYy9qUnkrS291YUZzR2FOWnc2bGNRVzE2YURGR0JwYjEx?=
 =?utf-8?B?U1BlZTFYdlZGVTdreXpGNFhzWDRIbFJLak4ybzJhNlhDZTRYbWFmQjVmbTVM?=
 =?utf-8?B?UTRtT1RwWUVtRGpaSVhQUGdJMWNpcGlVVFhCaWh4UDNYN09neE81M1FpRWlB?=
 =?utf-8?B?Tkx3Y1RhVWZLV200Vkp6TW1iV3JEdzZzWFBuc0VIUmNBWC9uL2NQdGQyWDFx?=
 =?utf-8?B?QkJKSTl3Ri9oV1JkcGZUVWlzdmFGd2x4QktVYTF4RWRwbm1jTldDQVRtbEJM?=
 =?utf-8?B?WmhuNDJ4a3dhOFJRejh4K0wyc2tVSmhBYnBaN25DaHpMNVBqN2ZMZE1zOGlv?=
 =?utf-8?B?ejRBdlZ3dC9icVgvbWZxaGl5ZW9SbzU1QjhzYVRHOFBiSU9jbzRRNVJ3L1gr?=
 =?utf-8?B?eDNRQ0dOOFdPcVUzeHYwaGRKUUJIejZDWXdsRTJMbUV1S04vTm56alVKNEJH?=
 =?utf-8?B?Zko5MENnR21UaUVZRjV5ekR5ZkJlcTRqR3dMcVEzOUdiYWhxWitjcXNHVkZG?=
 =?utf-8?B?WFdoazRVTU5ZWVNwTXRINUZSM2FQUWFrdmV4UG9HczFqWHY4a1JDT2hGRlh2?=
 =?utf-8?B?c0J5NGNWSlFFNU5MTlkyN2h2Uks0Q21yZ1JMb0ZXeGdhemI3TVdhZzgxTzB1?=
 =?utf-8?B?VC9VYTl6bjY2ajJiVm4zTTJVM0MzZWVwTW80bjFVWkd0MkErcm10NXRkOU5X?=
 =?utf-8?B?YW5MdXVBL1h6dUJFTCtLWDd1TmZaOTVNTWxiOENEMXd3M1hjNmpLVGRFR3Vi?=
 =?utf-8?B?SWJ3YkpYVEtjcVJMT2FzRkY1S3BXRmtkYnBiMVcrcFE0eXc0NDlwdVFhTklU?=
 =?utf-8?B?d1NtdVFISG1xYmMyK21DVUYyT2hxOXUxVTNtTFBBeWlpbngrTmFpbFNZdXEx?=
 =?utf-8?B?YW9rQmZpeXFwSjNJNHJ3bU9SM3BySWtTT3REa1pxK2lYYzJFSEpPK3I4UTRv?=
 =?utf-8?B?M1ErRS9hMWp5TUdoL3dpeGowSVIrZ093WTZrRnIzRjN3Zmo2VjVmOW9XWWJ1?=
 =?utf-8?B?TERuT3o3dkh2WXg5clgrT2JFbTA5YVZvUjBTTEdtR2tVZm85eEFOeHpralMy?=
 =?utf-8?B?MnpuUHFwTGxLQ1RZU3doUzNwWHhzenA5Rml1T2FPanpVdmRBajBGb0VuZC9E?=
 =?utf-8?B?KzVXb1NEMStzcEM4dFZSRFlIb0graWE2eEVla0FpTTZSNmxtK1ZHaGVaNDRF?=
 =?utf-8?B?Rkk5cmY0bkVvVys1QUUzK0FCOW1kREMrRWNUbmE2R3ZCbk9wTDFlb2FpRnll?=
 =?utf-8?B?d0k4STBqc0wyK3dnOGluZTYzOVcyNFNsMGhlZkJMdFd5T3BNNjJlbkc3b1h3?=
 =?utf-8?B?V1d3MWdGNDk2RkF5SmFzQWFnbVc1dUM2MjZvSWdTNDdCbW80MDJUZytGT3dK?=
 =?utf-8?B?Y3R0cXlHb3NEY0RmMk55S0tFSm53SUFkVnk2aUNiNUNDZE4rSy9CWGZ6QUpj?=
 =?utf-8?B?YWJZNXNJV0w3RkJLeVB4RnRpYVpHMWpGajZqcFhDbU04cW1GRy9uUXFiWGdM?=
 =?utf-8?B?b3h3akFmcVlCMU5HUHluSEU0WWhkWGUxREF2Mzg5bzlzSTVyMWVQR3ZrMFBP?=
 =?utf-8?B?UU1CMVg4OVJJL3NUK3JqUXcwdnNWdXNPaURYeFk5NHJRaUptd0lqK2NwbkFC?=
 =?utf-8?B?U21QVkIxZFZTZ09reHNVZG12MFNMZklQd2hYeGo1elFnWGgwbTR1Q3I5Wmpu?=
 =?utf-8?B?NExZUy9YREt4NGpMWllvY2dKZmt3TERSa1JLbjBIelk2RWpMOXFiQTYycXZt?=
 =?utf-8?B?MDVHQWI3RzNlMlV2ZWZSNE9hQkdIYU5PWHJ3MXUzYzVydXhUWnZxWDJJUWsy?=
 =?utf-8?B?U0xKZmFUaS9XdldmK2ViWVlwTEVNWndCRTFjQ3o2ZWZCR0gzRnQ3U0RJeTJ1?=
 =?utf-8?B?aFltZWtOa3lZVHhpcEVsT2pOYml2MmVBYUhtMlBRTnhGaGs5MzRzeUhMNnFZ?=
 =?utf-8?B?UFZZQ0EwUWoxTzg3ZEhBYkEzWUVHdWl0eVhTTzM3TGd4aW5lSk5EUGRNeUNV?=
 =?utf-8?B?aytxN0c1MW52VTlVMENJY1ZIc2w5SG5ha1d4WjY1Nm1sVGtIRWh6bjdyWnhZ?=
 =?utf-8?Q?eRX2daN4QMUWuWORtIbd5stl+weP6mPvOmGv0?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: b8c032b0-e741-4c80-f5ec-08da140e6751
X-MS-Exchange-CrossTenant-AuthSource: CO1PR10MB4531.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Apr 2022 18:35:32.3587
 (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: 8BvS8TG4CdccstvB+5ItAJYL+PKAG48h4Zxdz8YL++PbqmHZ409KmGpJS6tJajaTillSZpvcK/cK1edYXpvP7eml2mD+7Z8IHmE6FcHcJyE=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR10MB2782
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.425,18.0.850
 definitions=2022-04-01_05:2022-03-30,2022-04-01 signatures=0
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 mlxlogscore=999
 phishscore=0 malwarescore=0 bulkscore=0 suspectscore=0 adultscore=0
 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2202240000 definitions=main-2204010088
X-Proofpoint-ORIG-GUID: BQp9-j8UK9N-CVzJBdMB1yGJEu57d5nj
X-Proofpoint-GUID: BQp9-j8UK9N-CVzJBdMB1yGJEu57d5nj
X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_LOW,
        RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,
        T_SCC_BODY_TEXT_LINE 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 3/31/22 06:10, Baoquan He wrote:
> On 03/03/22 at 11:27am, Eric DeVolder wrote:
>> For kexec_file_load support, the loading of the crash kernel occurs
>> entirely within the kernel, and as such the elfcorehdr is readily
>> identified (so that it can be modified upon hotplug events).
>>
>> This change enables support for kexec_load by identifying the
>> elfcorehdr segment in the arch_crash_hotplug_handler(), if it has
>> not already been identified.
>>
>> In general, support for kexec_load requires corresponding changes
>> to the userspace kexec-tools utility. It is the responsibility of
>> the userspace kexec utility to ensure that:
>>   - the elfcorehdr segment is sufficiently large enough to accommodate
>>     hotplug changes, ala CRASH_HOTPLUG_ELFCOREHDR_SZ.
>>   - provides a purgatory that excludes the elfcorehdr from its list of
>>     run-time segments to check.
>> These changes to the userspace kexec utility are available, but not
>> yet accepted upstream.
> 
> These backgroud information should be put in cover letter, or in patch
> where they won't be grabbed into the final commit log.
Removed.

> 
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
> Here, if you want to put some status or backgroud information and expect
> they are not got into log, this is a appropriate place.
> 
> 
>>   arch/x86/kernel/crash.c | 26 ++++++++++++++++++++++++++
>>   1 file changed, 26 insertions(+)
>>
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 5da30e2bc780..45cc6e3af63e 100644
>> --- a/arch/x86/kernel/crash.c
>> +++ b/arch/x86/kernel/crash.c
>> @@ -486,6 +486,32 @@ void arch_crash_hotplug_handler(struct kimage *image,
>>   	void *elfbuf = NULL;
>>   	unsigned long mem, memsz;
>>   
>> +	/*
>> +	 * When the struct kimage is alloced, it is wiped to zero, so
>> +	 * the elf_index_valid defaults to false. It is set on the
>> +	 * kexec_file_load path, or here for kexec_load.
> 
>           I would make the last line as:
> 	 kexec_file_load path, or here for kexec_load if not already
>           identified..
done

> 
>> +	 */
>> +	if (!image->elf_index_valid) {
>> +		unsigned int n;
>> +
>> +		for (n = 0; n < image->nr_segments; n++) {
>> +			mem = image->segment[n].mem;
>> +			memsz = image->segment[n].memsz;
>> +			ptr = map_crash_pages(mem, memsz);
>> +			if (ptr) {
>> +				/* The segment containing elfcorehdr */
>> +				if ((ptr[0] == 0x7F) &&
>> +					(ptr[1] == 'E') &&
>> +					(ptr[2] == 'L') &&
>> +					(ptr[3] == 'F')) {
> 
> Can it be like memcmp(ptr, ELFMAG, SELFMAG) as we have done in
> parse_crash_elf_headers()? With that, one line is taken.
done

> 
>> +					image->elf_index = (int)n;
>> +					image->elf_index_valid = true;
>> +				}
>> +			}
>> +			unmap_crash_pages((void **)&ptr);
>> +		}
>> +	}
>> +
>>   	/* Must have valid elfcorehdr index */
>>   	if (!image->elf_index_valid) {
>>   		pr_err("crash hp: unable to locate elfcorehdr segment");
>> -- 
>> 2.27.0
>>
>