Re: [PATCH v14 3/7] crash: add generic infrastructure for crash hotplug support

Eric DeVolder
2022-11-28T15:47:43Z

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
>>
>