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Message-ID: <248486ff-5f9d-bffd-ab6e-131c54f31bd8@oracle.com>
Date:   Mon, 28 Nov 2022 09:46:34 -0600
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Subject: Re: [PATCH v14 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: <20221116214643.6384-1-eric.devolder@oracle.com>
 <20221116214643.6384-4-eric.devolder@oracle.com>
 <Y4A1/cSekXUTFriC@MiWiFi-R3L-srv>
From:   Eric DeVolder <eric.devolder@oracle.com>
In-Reply-To: <Y4A1/cSekXUTFriC@MiWiFi-R3L-srv>
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On 11/24/22 21:26, Baoquan He wrote:
> On 11/16/22 at 04:46pm, Eric DeVolder wrote:
> ......
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index ebf46c3b8f8b..b4dbc21f9081 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -32,6 +32,7 @@ extern note_buf_t __percpu *crash_notes;
>>   #include <linux/compat.h>
>>   #include <linux/ioport.h>
>>   #include <linux/module.h>
>> +#include <linux/highmem.h>
>>   #include <asm/kexec.h>
>>   
>>   /* Verify architecture specific macros are defined */
>> @@ -374,6 +375,13 @@ struct kimage {
>>   	struct purgatory_info purgatory_info;
>>   #endif
>>   
>> +#ifdef CONFIG_CRASH_HOTPLUG
> 
> This kernel config CRASH_HOTPLUG is added in patch 7, but we have used
> it in the previous patch, not sure if this is acceptable.
> 
I wasn't sure what to do here either. Patch 7 is the x86 arch-specific support patch, and 
CRASH_HOTPLUG is introduced in arch/x86/Kconfig. I did look at introducing CRASH_HOTPLUG as a 
generic/non-arch-specific option, but no location seemed appropriate given HOTPLUG_CPU is 
arch-specific and MEMORY_HOTPLUG is in mm/Kconfig.

This doesn't break bisect, but as you point out, not sure if the location in patch 7 is acceptable.
I'm not really sure how to resolve the question.

eric

>> +	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 +511,34 @@ 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
>> +/*
>> + * NOTE: The addresses and sizes passed to this routine have
>> + * already been fully aligned on page boundaries. There is no
>> + * need for massaging the address or size.
>> + */
>> +static inline void *arch_map_crash_pages(unsigned long paddr,
>> +					unsigned long size)
>> +{
>> +	if (size > 0)
>> +		return kmap_local_page(pfn_to_page(paddr >> PAGE_SHIFT));
>> +	else
>> +		return NULL;
>> +}
>> +#endif
>> +
>> +#ifndef arch_unmap_crash_pages
>> +static inline void arch_unmap_crash_pages(void *ptr)
>> +{
>> +	if (ptr)
>> +		kunmap_local(ptr);
>> +}
>> +#endif
>> +
>> +#ifndef arch_crash_handle_hotplug_event
>> +static inline void arch_crash_handle_hotplug_event(struct kimage *image) { }
>> +#endif
>> +
>>   #else /* !CONFIG_KEXEC_CORE */
>>   struct pt_regs;
>>   struct task_struct;
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 8c648fd5897a..4e7221226976 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;
>> @@ -612,3 +615,139 @@ static int __init crash_save_vmcoreinfo_init(void)
>>   }
>>   
>>   subsys_initcall(crash_save_vmcoreinfo_init);
>> +
>> +#ifdef CONFIG_CRASH_HOTPLUG
>> +#undef pr_fmt
>> +#define pr_fmt(fmt) "crash hp: " fmt
>> +/*
>> + * 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 size
>> + * is based on NR_CPUS_DEFAULT and 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 */
>> +	if (kexec_trylock()) {
>> +
>> +		/* 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("hp_action %u, cpu %u\n", hp_action, cpu);
>> +			else
>> +				pr_debug("hp_action %u\n", hp_action);
>> +
>> +			/*
>> +			 * When the struct kimage is allocated, it is wiped to zero, so
>> +			 * 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 long mem, memsz;
>> +				unsigned char *ptr;
>> +				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);
>> +					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("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);
>> +
>> +			/* 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 */
>> +		kexec_unlock();
>> +	}
>> +}
>> +
>> +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,
>> +			KEXEC_CRASH_HP_INVALID_CPU);
>> +		break;
>> +
>> +	case MEM_OFFLINE:
>> +		handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY,
>> +			KEXEC_CRASH_HP_INVALID_CPU);
>> +		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
>>
>