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Date:   Wed, 31 Aug 2022 12:24:29 -0500
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Subject: Re: [PATCH v11 3/7] crash: add generic infrastructure for crash
 hotplug support
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,
        sourabhjain@linux.ibm.com, konrad.wilk@oracle.com,
        boris.ostrovsky@oracle.com
References: <20220826173704.1895-1-eric.devolder@oracle.com>
 <20220826173704.1895-4-eric.devolder@oracle.com>
 <Yw7U5jYKcwZ+cMpu@MiWiFi-R3L-srv>
From:   Eric DeVolder <eric.devolder@oracle.com>
In-Reply-To: <Yw7U5jYKcwZ+cMpu@MiWiFi-R3L-srv>
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On 8/30/22 22:26, Baoquan He wrote:
> On 08/26/22 at 01:37pm, Eric DeVolder wrote:
>> CPU and memory change notifications are received in order to
>> regenerate the elfcorehdr.
>>
>> To support cpu hotplug, a callback is registered to capture the
>> CPUHP_AP_ONLINE_DYN online and offline events via
>> cpuhp_setup_state_nocalls().
>>
>> To support memory hotplug, a notifier is registered to capture the
>> MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().
>>
>> The cpu callback and memory notifiers call handle_hotplug_event()
>> which performs needed tasks and then dispatches the event to the
>> architecture specific arch_crash_handle_hotplug_event(). During the
>> process, the kexec_mutex is held.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   include/linux/crash_core.h |   8 +++
>>   include/linux/kexec.h      |  26 +++++++
>>   kernel/crash_core.c        | 134 +++++++++++++++++++++++++++++++++++++
>>   3 files changed, 168 insertions(+)
>>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index de62a722431e..3b99e69b011f 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -84,4 +84,12 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
>>   int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
>>   		unsigned long long *crash_size, unsigned long long *crash_base);
>>   
>> +#define KEXEC_CRASH_HP_REMOVE_CPU		0
>> +#define KEXEC_CRASH_HP_ADD_CPU			1
>> +#define KEXEC_CRASH_HP_REMOVE_MEMORY	2
>                                          ~~
>                                          Nitpick, These arenot aligned,

done!

>> +#define KEXEC_CRASH_HP_ADD_MEMORY		3
>> +#define KEXEC_CRASH_HP_INVALID_CPU		-1U
>> +
>> +struct kimage;
>> +
>>   #endif /* LINUX_CRASH_CORE_H */
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index 4eefa631e0ae..9597b41136ec 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -374,6 +374,13 @@ struct kimage {
>>   	struct purgatory_info purgatory_info;
>>   #endif
>>   
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +	bool hotplug_event;
>> +	unsigned int offlinecpu;
>> +	bool elfcorehdr_index_valid;
>> +	int elfcorehdr_index;
>> +#endif
>> +
>>   #ifdef CONFIG_IMA_KEXEC
>>   	/* Virtual address of IMA measurement buffer for kexec syscall */
>>   	void *ima_buffer;
>> @@ -503,6 +510,25 @@ static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, g
>>   static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }
>>   #endif
>>   
>> +#ifndef arch_map_crash_pages
>> +static inline void *arch_map_crash_pages(unsigned long paddr,
>> +		unsigned long size)
>> +{
>> +	return NULL;
>> +}
>> +#endif
>> +
>> +#ifndef arch_unmap_crash_pages
>> +static inline void arch_unmap_crash_pages(void **ptr) { }
>> +#endif
>> +
>> +#ifndef arch_crash_handle_hotplug_event
>> +static inline void arch_crash_handle_hotplug_event(struct kimage *image,
>> +		unsigned int hp_action)
>> +{
>> +}
>> +#endif
>> +
>>   #else /* !CONFIG_KEXEC_CORE */
>>   struct pt_regs;
>>   struct task_struct;
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 0f8aa659cca4..455150205ded 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -11,6 +11,8 @@
>>   #include <linux/vmalloc.h>
>>   #include <linux/sizes.h>
>>   #include <linux/kexec.h>
>> +#include <linux/memory.h>
>> +#include <linux/cpuhotplug.h>
>>   
>>   #include <asm/page.h>
>>   #include <asm/sections.h>
>> @@ -18,6 +20,7 @@
>>   #include <crypto/sha1.h>
>>   
>>   #include "kallsyms_internal.h"
>> +#include "kexec_internal.h"
>>   
>>   /* vmcoreinfo stuff */
>>   unsigned char *vmcoreinfo_data;
>> @@ -611,3 +614,134 @@ static int __init crash_save_vmcoreinfo_init(void)
>>   }
>>   
>>   subsys_initcall(crash_save_vmcoreinfo_init);
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +/*
>> + * To accurately reflect hot un/plug changes, the elfcorehdr (which
>> + * is passed to the crash kernel via the elfcorehdr= parameter)
>> + * must be updated with the new list of CPUs and memories.
>> + *
>> + * In order to make changes to elfcorehdr, two conditions are needed:
>> + * First, the segment containing the elfcorehdr must be large enough
>> + * to permit a growing number of resources. The elfcorehdr memory is
>> + * typically based on CONFIG_NR_CPUS and CONFIG_CRASH_MAX_MEMORY_RANGES.
>> + * Second, purgatory must explicitly exclude the elfcorehdr from the
>> + * list of segments it checks (since the elfcorehdr changes and thus
>> + * would require an update to purgatory itself to update the digest).
>> + */
>> +static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
>> +{
>> +	/* Obtain lock while changing crash information */
>> +	mutex_lock(&kexec_mutex);
>> +
>> +	/* Check kdump is loaded */
>> +	if (kexec_crash_image) {
>> +		struct kimage *image = kexec_crash_image;
>> +
>> +		if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
>> +			hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
>> +			pr_debug("crash hp: hp_action %u, cpu %u\n", hp_action, cpu);
>> +		else
>> +			pr_debug("crash hp: hp_action %u", hp_action);
>                                                         ^~ "\n" missed
done!

>> +		/*
>> +		 * When the struct kimage is alloced, it is wiped to zero, so
>                                               ~~~~ alloced is confusing, s/alloced/allocated/
>                                              We can accept alloc being used, alloced is a little weird.

done!

>> +		 * the elfcorehdr_index_valid defaults to false. Find the
>> +		 * segment containing the elfcorehdr, if not already found.
>> +		 * This works for both the kexec_load and kexec_file_load paths.
>> +		 */
>> +		if (!image->elfcorehdr_index_valid) {
>> +			unsigned char *ptr;
>> +			unsigned long mem, memsz;
>> +			unsigned int n;
>> +
>> +			for (n = 0; n < image->nr_segments; n++) {
>> +				mem = image->segment[n].mem;
>> +				memsz = image->segment[n].memsz;
>> +				ptr = arch_map_crash_pages(mem, memsz);
> OK, I see. You want to avoid the over 80 chars line, so introducing
> two local variables. We may be able to tolerate that in this case. No
> strong opinion, let's see if other people have concern about it.
> 
> Other than these nitpicks, this patch looks good to me.
> Acked-by: Baoquan He <bhe@redhat.com>

Thank you!
eric

> 
>> +				if (ptr) {
>> +					/* The segment containing elfcorehdr */
>> +					if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
>> +						image->elfcorehdr_index = (int)n;
>> +						image->elfcorehdr_index_valid = true;
>> +					}
>> +				}
>> +				arch_unmap_crash_pages((void **)&ptr);
>> +			}
>> +		}
>> +
>> +		if (!image->elfcorehdr_index_valid) {
>> +			pr_err("crash hp: unable to locate elfcorehdr segment");
>> +			goto out;
>> +		}
>> +
>> +		/* Needed in order for the segments to be updated */
>> +		arch_kexec_unprotect_crashkres();
>> +
>> +		/* Flag to differentiate between normal load and hotplug */
>> +		image->hotplug_event = true;
>> +
>> +		/* Now invoke arch-specific update handler */
>> +		arch_crash_handle_hotplug_event(image, hp_action);
>> +
>> +		/* No longer handling a hotplug event */
>> +		image->hotplug_event = false;
>> +
>> +		/* Change back to read-only */
>> +		arch_kexec_protect_crashkres();
>> +	}
>> +
>> +out:
>> +	/* Release lock now that update complete */
>> +	mutex_unlock(&kexec_mutex);
>> +}
>> +
>> +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
>> +{
>> +	switch (val) {
>> +	case MEM_ONLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
>> +		break;
>> +
>> +	case MEM_OFFLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
>> +		break;
>> +	}
>> +	return NOTIFY_OK;
>> +}
>> +
>> +static struct notifier_block crash_memhp_nb = {
>> +	.notifier_call = crash_memhp_notifier,
>> +	.priority = 0
>> +};
>> +
>> +static int crash_cpuhp_online(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int crash_cpuhp_offline(unsigned int cpu)
>> +{
>> +	handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
>> +	return 0;
>> +}
>> +
>> +static int __init crash_hotplug_init(void)
>> +{
>> +	int result = 0;
>> +
>> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>> +		register_memory_notifier(&crash_memhp_nb);
>> +
>> +	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
>> +		result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> +						   "crash/cpuhp",
>> +						   crash_cpuhp_online,
>> +						   crash_cpuhp_offline);
>> +
>> +	return result;
>> +}
>> +
>> +subsys_initcall(crash_hotplug_init);
>> +#endif
>> -- 
>> 2.31.1
>>
>