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Message-ID: <0bccf3c8-10b2-d4cc-0474-fde41145d568@oracle.com>
Date: Wed, 31 Aug 2022 12:24:29 -0500
From: Eric DeVolder <eric.devolder@...cle.com>
To: Baoquan He <bhe@...hat.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
kexec@...ts.infradead.org, ebiederm@...ssion.com,
dyoung@...hat.com, vgoyal@...hat.com, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
boris.ostrovsky@...cle.com
Subject: Re: [PATCH v11 3/7] crash: add generic infrastructure for crash
hotplug support
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@...cle.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@...hat.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
>>
>
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