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

Baoquan He
2022-11-25T03:28:00Z

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.

> + 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
>