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: <c15e968f-c23f-b41f-1fa3-10ad16f6fb35@oracle.com>
Date:   Thu, 8 Dec 2022 14:34:47 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.3.1
Subject: Re: [PATCH v14 7/7] x86/crash: add x86 crash hotplug support
Content-Language: en-US
To:     Borislav Petkov <bp@alien8.de>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com,
        tglx@linutronix.de, mingo@redhat.com, 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,
        sourabhjain@linux.ibm.com, konrad.wilk@oracle.com,
        boris.ostrovsky@oracle.com
References: <20221116214643.6384-1-eric.devolder@oracle.com>
 <20221116214643.6384-8-eric.devolder@oracle.com> <Y5BozkPot12L5d9w@zn.tnic>
From:   Eric DeVolder <eric.devolder@oracle.com>
In-Reply-To: <Y5BozkPot12L5d9w@zn.tnic>
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?RDZ1SlQ3cndKY0RZT0grZDNZSVJ1VGRhbHJJcTFtNWFNVEMwMEhDbGVET2pJ?=
 =?utf-8?B?R0thMFpRK1JFK0tBV0dSUy9OMzhmdjFrc0xpb2x2eEljbUxHQmxOYjFUOU5P?=
 =?utf-8?B?R2MzYnB3NWxPajF2Zk85NlhkQ3BOYVpwZmFkOFVLdnJPTG11OE4yTWlGMWRu?=
 =?utf-8?B?TEMvWXYvdEE0NkxRNlJHMXVRQ0hpSG9SWUNoQlA5SWlnemNIY3lYUmlTOVhD?=
 =?utf-8?B?N3ltM08wOG8vbWZxY2FHTjViNzNxay9GV3JZTThuaXFWRmlwaG9hMWo1T1lM?=
 =?utf-8?B?UnVMcGE3L1dVckxrcXFxR2gxbXBiMlMyeDdScVNSQTZRSjM1ZUtlZXhBRkp3?=
 =?utf-8?B?V0JxaklmNlJobDlLZ0dIeGh1b0ZaSEFHdHljall2NGFEOWVoYS9WOTZwTlU2?=
 =?utf-8?B?RjA5R3dJQ3lWYURJbGlkZEs3NFZCbU5mN0NUM2RxM2RYM0o2N0NXajMwQVll?=
 =?utf-8?B?NG1ETXNrVGVOVkRKQVBYKzZFOWpPUWhDVEo4Qmt6L2s3d1Rid1ZyU0hmWm9X?=
 =?utf-8?B?TGE2Ym1iQnRrU0RuUHY5QW5mOU5jN25VK1RzOFhHMWo0ZnQyZWNydXJFOGQ2?=
 =?utf-8?B?SGpTNXRQdDVXa1dGVTU2SHFFQ20vMTE3SGFoYXJYQWFWMkVhRmg2VUZRdVNZ?=
 =?utf-8?B?Q1RQMmRwYmFMcGI3RFJjSlgvbHZDNXRjck5BYm1LNzNrRWRtTXVuNzRzZ29T?=
 =?utf-8?B?TUdKRHcyQitsK1VFbGJrZ294dEZnUVBkdENUWFRiQ3VzWmNBaE9raHdrUTVv?=
 =?utf-8?B?eWl1R1dGTk1GY2g5a2RxcXZ6NWh5WFhhcXVaT25OTFBYQWQrRllkQitMajNv?=
 =?utf-8?B?a0s0aWowVnMxNVU1MXBHRUhXV0JPNUpZYlE0czlJTGhWcHliNzk5ZU1ZVUZu?=
 =?utf-8?B?TUxvdjVvTkNuRGVHTU41OFZjaUhhd3JwUmt4YlB5WkRYUnJvSFZNRHdIaU1w?=
 =?utf-8?B?QUNGdEtad2JDMzZoOEhPZDM2T3Q5T3dVWDNLdGI2dVRCVml4dlljV1hXekFy?=
 =?utf-8?B?V0VBNkwxZ0VJdHdlZEpsYnAzRkZhNG5rTG1uaVUwNE1wKzF3ZHQ4bkkwbmlt?=
 =?utf-8?B?OW9TVUlWaGhpaGtTRmRWbTVEK0tKZVNpd3RMUTZweE94cVZvMm1uSDMySjRl?=
 =?utf-8?B?UVltSGJESnZFcWFuNWk4NXVmUWdDNHMwNWs0M0ZMUloyb2lYd2xuYjk5ajls?=
 =?utf-8?B?TjFDODBjbUEwa0VKUVRYNTdKc2k5QnNzVFpXQkpCS1dwTDBwMm1URmxnMitr?=
 =?utf-8?B?WVFpMlhhMDgxNUJuVjZTd0VJTWF6d2szdUxEMDVpV2NOZWVwcGU1aWFhTVk1?=
 =?utf-8?B?cHR0MVBZU3hyQWtGaU53SHBvQ0hnd1ZTZ2hiZlpVcngyczBocHVxSDVrQ2gv?=
 =?utf-8?B?em9TUWlIdW55T1FsTjJrVENnblBLYXV4UzB2L0RiYlloN0o4bnFtbGhzRnh1?=
 =?utf-8?B?S2hIbGhVZ0U4Qm1Qa0VUQ2FVZUU2OW9rby96QUpnT1h4eTZqd3NaME14YUFM?=
 =?utf-8?B?d3ZjRW40OHlMQ3dTaWdjMmV5VHR3ZzdoK2pTNE9WUGhMZzVTTXBUUkNRZDhj?=
 =?utf-8?B?QWozWGVoYXFmdVJNSGh4bjU1c0QxVTdGWkc0OVdMUEJnVEUwMG5JYlFubTFG?=
 =?utf-8?B?a1dKazVIZGJxdkhEd2hiRXFsTDgzTmtqR0NIdHFLSzQ4SWhFTWJjSEk5TDk4?=
 =?utf-8?B?R2VBT0pqZVkyVVkrV2ZlRnlCcDlGVTNxRVVLUmxyTldvQlp4SldCRldGMVk4?=
 =?utf-8?B?UUpXbkVIYnE2dXZUY3Q1WjkzcnduZDdUVzdPd004VGgxMS9ZSWJQTDNVSTFB?=
 =?utf-8?B?U3QrMDNCejZDL0I0dXYxMmRZOGp5ZVJDcW1NNTZ0UTAwNm9mQVF4SnE4NzNK?=
 =?utf-8?B?aEdHbXRVV0dUa3k0MExFNG9KZytaRENLRkdVVi9pQlFqcVkzTFo2WjBLNUE2?=
 =?utf-8?B?ZmlscW03WlNveHVZc24xbHcybkhzRmFJSWZKVjQwbmFYaTVpWlpTRHBQWHdr?=
 =?utf-8?B?aDJTSG85ak16UUhwUWRaNHhYZHQ4M1lwNHc1YWZBOURXUjgyemFXblhmQkhh?=
 =?utf-8?B?SVRsekxoWmQwUlpXQlBmSUlCVVFXL3AxUml2ZXZObmFQRVAxVXluakRVVVBC?=
 =?utf-8?B?UVRkVVY4eDlIanM2YnpVWTB1b1BDRnpWaWowZG5ibW1XcjF6WktHSG5mSHlz?=
 =?utf-8?Q?a7DOfZL5dz25ICTy9v36IOY=3D?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 70858403-3c15-4345-e22c-08dad95bab34
X-MS-Exchange-CrossTenant-AuthSource: CO1PR10MB4531.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Dec 2022 20:34:57.8198
 (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: VR9yuq2MmoQ6JL4Tsy9vivXqWyMNiUhKiyeUiowTlZDpjGSu6fxc/LuOOX7xPhLWLcAZqZ+DFE1QmEWja0asXYKINv6HaWjQX4Jfg6pM/cI=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR10MB6786
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.205,Aquarius:18.0.923,Hydra:6.0.545,FMLib:17.11.122.1
 definitions=2022-12-08_11,2022-12-08_01,2022-06-22_01
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 bulkscore=0
 suspectscore=0 phishscore=0 malwarescore=0 mlxscore=0 spamscore=0
 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2210170000 definitions=main-2212080171
X-Proofpoint-GUID: wDqn6ndjmfsTmnj6rj7I_A_sI-3u9hkt
X-Proofpoint-ORIG-GUID: wDqn6ndjmfsTmnj6rj7I_A_sI-3u9hkt
X-Spam-Status: No, score=-3.1 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_H2,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-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 12/7/22 04:19, Borislav Petkov wrote:
> On Wed, Nov 16, 2022 at 04:46:43PM -0500, Eric DeVolder wrote:
>> When CPU or memory is hot un/plugged, the crash elfcorehdr, which
>> describes the CPUs and memory in the system, must also be updated.
>>
>> A new elfcorehdr is generated from the available CPUs and memory
>> into a buffer, and then installed over the top of the existing
>> elfcorehdr. The segment containing the elfcorehdr is identified
>> at run time in crash_core:handle_hotplug_event(), which works for
>> both the kexec_load() and kexec_file_load() syscalls.
>>
>> In the patch 'kexec: exclude elfcorehdr from the segment digest'
>> the need to update purgatory due to the change in elfcorehdr was
>> eliminated.  As a result, no changes to purgatory or boot_params
>> (as the elfcorehdr= kernel command line parameter pointer
>> remains unchanged and correct) are needed, just elfcorehdr.
>>
>> To accommodate a growing number of resources via hotplug, the
>> elfcorehdr segment must be sufficiently large enough to accommodate
>> changes, see the CRASH_MAX_MEMORY_RANGES description.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   arch/x86/Kconfig             |   9 +++
>>   arch/x86/include/asm/kexec.h |  15 +++++
>>   arch/x86/kernel/crash.c      | 106 ++++++++++++++++++++++++++++++++++-
>>   3 files changed, 127 insertions(+), 3 deletions(-)
> 
> Some quick cleanups ontop, there's potential for more:
> 
> ---
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index ffee99046942..486509030d3a 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2091,13 +2091,16 @@ config CRASH_DUMP
>   	  For more details see Documentation/admin-guide/kdump/kdump.rst
>   
>   config CRASH_HOTPLUG
> -	bool "kernel updates of crash elfcorehdr"
> +	bool "Update the crash elfcorehdr on system configuration changes"
>   	default n
>   	depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG)
>   	help
> -	  Enable the kernel to directly update the crash elfcorehdr (which
> -	  contains the list of CPUs and memory regions to be dumped upon
> -	  a crash) in response to hot plug/unplug of CPUs or memory.
> +	  Enable direct updates to the crash elfcorehdr (which contains
> +	  the list of CPUs and memory regions to be dumped upon a crash)
> +	  in response to hot plug/unplug of CPUs or memory. This is a much
> +	  more advanced approach than userspace attempting that.
> +
> +	  If unsure, say Y.
Done!

>   
>   config KEXEC_JUMP
>   	bool "kexec jump"
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index d2238bcf8106..d26f208e582e 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -413,25 +413,32 @@ int crash_load_segments(struct kimage *image)
>   	image->elf_headers_sz	= kbuf.bufsz;
>   	kbuf.memsz		= kbuf.bufsz;
>   
> -#ifdef CONFIG_CRASH_HOTPLUG
> -	/* Ensure elfcorehdr segment large enough for hotplug changes */
> -	unsigned long pnum = 2; /* VMCOREINFO and kernel_map */
> -
> -	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
> -		pnum += CONFIG_NR_CPUS_DEFAULT;
> -	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> -		pnum += CRASH_MAX_MEMORY_RANGES;
> -	if (pnum < (unsigned long)PN_XNUM) {
> -		kbuf.memsz = pnum * sizeof(Elf64_Phdr);
> -		kbuf.memsz += sizeof(Elf64_Ehdr);
> -		image->elfcorehdr_index = image->nr_segments;
> -		image->elfcorehdr_index_valid = true;
> -		/* Mark as usable to crash kernel, else crash kernel fails on boot */
> -		image->elf_headers_sz = kbuf.memsz;
> -	} else {
> -		pr_err("number of Phdrs %lu exceeds max\n", pnum);
> +	if (IS_ENABLED(CONFIG_CRASH_HOTPLUG)) {
> +		/*
> +		 * Ensure the elfcorehdr segment large enough for hotplug changes.
> +		 * Start with VMCOREINFO and kernel_map:
> +		 */
> +		unsigned long pnum = 2;
> +
> +		if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
> +			pnum += CONFIG_NR_CPUS_DEFAULT;
> +
> +		if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> +			pnum += CRASH_MAX_MEMORY_RANGES;
> +
> +		if (pnum < (unsigned long)PN_XNUM) {
> +			kbuf.memsz = pnum * sizeof(Elf64_Phdr);
> +			kbuf.memsz += sizeof(Elf64_Ehdr);
> +
> +			image->elfcorehdr_index = image->nr_segments;
> +			image->elfcorehdr_index_valid = true;
> +
> +			/* Mark as usable to crash kernel, else crash kernel fails on boot */
> +			image->elf_headers_sz = kbuf.memsz;
> +		} else {
> +			pr_err("number of Phdrs %lu exceeds max\n", pnum);
> +			}
Done, converted this block to an IS_ENABLED(CONFIG_CRASH_HOTPLUG).

>   	}
> -#endif
>   
>   	kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
>   	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
> @@ -463,10 +470,9 @@ int crash_load_segments(struct kimage *image)
>    */
>   void arch_crash_handle_hotplug_event(struct kimage *image)
>   {
> +	void *elfbuf, *old_elfcorehdr;
>   	unsigned long mem, memsz;
> -	unsigned long elfsz = 0;
> -	void *elfbuf = NULL;
> -	void *ptr;
> +	unsigned long elfsz;
Done, note that I leave elfbuf initialized to NULL as its use in prepare_elf_headers() does not 
necessarily write it, so it could otherwise have been used uninitialized.

>   
>   	/*
>   	 * Create the new elfcorehdr reflecting the changes to CPU and/or
> @@ -489,26 +495,24 @@ void arch_crash_handle_hotplug_event(struct kimage *image)
>   		goto out;
>   	}
>   
> -	/*
> -	 * Copy new elfcorehdr over the old elfcorehdr at destination.
> -	 */
> -	ptr = arch_map_crash_pages(mem, memsz);
> -	if (ptr) {
> -		/*
> -		 * Temporarily invalidate the crash image while the
> -		 * elfcorehdr is updated.
> -		 */
> -		xchg(&kexec_crash_image, NULL);
> -		memcpy_flushcache(ptr, elfbuf, elfsz);
> -		xchg(&kexec_crash_image, image);
> -		arch_unmap_crash_pages(ptr);
> -		pr_debug("updated elfcorehdr\n");
> -	} else {
> +	/* Copy new elfcorehdr over the old elfcorehdr at destination. */
> +	old_elfcorehdr = arch_map_crash_pages(mem, memsz);
> +	if (!old_elfcorehdr) {
>   		pr_err("updating elfcorehdr failed\n");
> +		goto out;
>   	}
Done, changed to old_elfcorehdr and error/early-out.

>   
> +	/*
> +	 * Temporarily invalidate the crash image while the elfcorehdr
> +	 * is updated.
> +	 * */
> +	xchg(&kexec_crash_image, NULL);
> +	memcpy_flushcache(old_elfcorehdr, elfbuf, elfsz);
> +	xchg(&kexec_crash_image, image);
> +	arch_unmap_crash_pages(old_elfcorehdr);
> +	pr_debug("updated elfcorehdr\n");
> +
>   out:
> -	if (elfbuf)
> -		vfree(elfbuf);
> +	vfree(elfbuf);
>   }
>   #endif
> 
Done.

Thanks!
eric