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    SubjectRe: [PATCH v7 4/8] crash: add generic infrastructure for crash hotplug support
    On 04/13/22 at 12:42pm, Eric DeVolder wrote:
    > Upon CPU and memory changes, a generic crash_hotplug_handler()
    > dispatches the hot plug/unplug event to the architecture specific
    > arch_crash_hotplug_handler(). During the process, the kexec_mutex
    > is held.
    >
    > To support cpu hotplug, a callback is registered to capture the
    > CPUHP_AP_ONLINE_DYN online and ofline 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 notifier then call crash_hotplug_handler()
    > to handle the hot plug/unplug event.
    >
    > Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
    > ---
    > include/linux/kexec.h | 16 +++++++
    > kernel/crash_core.c | 101 ++++++++++++++++++++++++++++++++++++++++++
    > 2 files changed, 117 insertions(+)
    >
    > diff --git a/include/linux/kexec.h b/include/linux/kexec.h
    > index f93f2591fc1e..02daff1f47dd 100644
    > --- a/include/linux/kexec.h
    > +++ b/include/linux/kexec.h
    > @@ -306,6 +306,13 @@ struct kimage {
    >
    > /* Information for loading purgatory */
    > struct purgatory_info purgatory_info;
    > +
    > +#ifdef CONFIG_CRASH_HOTPLUG
    > + bool hotplug_event;
    > + unsigned int offlinecpu;
    > + bool elfcorehdr_index_valid;
    > + int elfcorehdr_index;
    > +#endif
    > #endif
    >
    > #ifdef CONFIG_IMA_KEXEC
    > @@ -322,6 +329,15 @@ struct kimage {
    > unsigned long elf_load_addr;
    > };
    >
    > +#ifdef CONFIG_CRASH_HOTPLUG
    > +void arch_crash_hotplug_handler(struct kimage *image,
    > + unsigned int hp_action, unsigned int cpu);
    > +#define KEXEC_CRASH_HP_REMOVE_CPU 0
    > +#define KEXEC_CRASH_HP_ADD_CPU 1
    > +#define KEXEC_CRASH_HP_REMOVE_MEMORY 2
    > +#define KEXEC_CRASH_HP_ADD_MEMORY 3
    > +#endif /* CONFIG_CRASH_HOTPLUG */
    > +
    > /* kexec interface functions */
    > extern void machine_kexec(struct kimage *image);
    > extern int machine_kexec_prepare(struct kimage *image);
    > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
    > index 256cf6db573c..ecf746243ab2 100644
    > --- a/kernel/crash_core.c
    > +++ b/kernel/crash_core.c
    > @@ -9,12 +9,17 @@
    > #include <linux/init.h>
    > #include <linux/utsname.h>
    > #include <linux/vmalloc.h>
    > +#include <linux/highmem.h>
    > +#include <linux/memory.h>
    > +#include <linux/cpuhotplug.h>
    >
    > #include <asm/page.h>
    > #include <asm/sections.h>
    >
    > #include <crypto/sha1.h>
    >
    > +#include "kexec_internal.h"
    > +
    > /* vmcoreinfo stuff */
    > unsigned char *vmcoreinfo_data;
    > size_t vmcoreinfo_size;
    > @@ -491,3 +496,99 @@ static int __init crash_save_vmcoreinfo_init(void)
    > }
    >
    > subsys_initcall(crash_save_vmcoreinfo_init);
    > +
    > +#ifdef CONFIG_CRASH_HOTPLUG
    > +void __weak arch_crash_hotplug_handler(struct kimage *image,
    > + unsigned int hp_action, unsigned int cpu)
    > +{
    > + pr_warn("crash hp: %s not implemented", __func__);
    > +}
    > +
    > +static void crash_hotplug_handler(unsigned int hp_action,
    > + unsigned int cpu)
    > +{
    > + /* Obtain lock while changing crash information */
    > + if (!mutex_trylock(&kexec_mutex))
    > + return;
    > +
    > + /* Check kdump is loaded */
    > + if (kexec_crash_image) {
    > + pr_debug("crash hp: hp_action %u, cpu %u", hp_action, cpu);
    > +
    > + /* Needed in order for the segments to be updated */
    > + arch_kexec_unprotect_crashkres();
    > +
    > + /* Flag to differentiate between normal load and hotplug */
    > + kexec_crash_image->hotplug_event = true;
    > +
    > + /* Now invoke arch-specific update handler */
    > + arch_crash_hotplug_handler(kexec_crash_image, hp_action, cpu);
    > +
    > + /* No longer handling a hotplug event */
    > + kexec_crash_image->hotplug_event = false;
    > +
    > + /* Change back to read-only */
    > + arch_kexec_protect_crashkres();
    > + }
    > +
    > + /* Release lock now that update complete */
    > + mutex_unlock(&kexec_mutex);
    > +}
    > +
    > +#if defined(CONFIG_MEMORY_HOTPLUG)
    > +static int crash_memhp_notifier(struct notifier_block *nb,
    > + unsigned long val, void *v)
    > +{
    > + struct memory_notify *mhp = v;
    > +
    > + switch (val) {
    > + case MEM_ONLINE:
    > + crash_hotplug_handler(KEXEC_CRASH_HP_ADD_MEMORY, -1U);
    We don't differentiate the memory add/remove, cpu add, except of cpu
    remove. Means the hp_action only differentiate cpu remove from the other
    action. Maybe only making two types?

    #define KEXEC_CRASH_HP_REMOVE_CPU 0
    #define KEXEC_CRASH_HP_UPDATE_OTHER 1

    And define a new macro to replace the magic number?

    #define KEXEC_CRASH_HP_INVALID_CPU -1U
    > + break;
    > +
    > + case MEM_OFFLINE:
    > + crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_MEMORY, -1U);
    > + break;
    > + }
    > + return NOTIFY_OK;
    > +}
    > +
    > +static struct notifier_block crash_memhp_nb = {
    > + .notifier_call = crash_memhp_notifier,
    > + .priority = 0
    > +};
    > +#endif
    > +
    > +#if defined(CONFIG_HOTPLUG_CPU)
    > +static int crash_cpuhp_online(unsigned int cpu)
    > +{
    > + crash_hotplug_handler(KEXEC_CRASH_HP_ADD_CPU, cpu);
    Should making the cpu as -1U?
    crash_hotplug_handler(KEXEC_CRASH_HP_ADD_CPU, -1U);
    > + return 0;
    > +}
    > +
    > +static int crash_cpuhp_offline(unsigned int cpu)
    > +{
    > + crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
    > + return 0;
    > +}
    > +#endif
    > +
    > +static int __init crash_hotplug_init(void)
    > +{
    > + int result = 0;
    > +
    > +#if defined(CONFIG_MEMORY_HOTPLUG)
    > + register_memory_notifier(&crash_memhp_nb);
    > +#endif
    > +
    > +#if defined(CONFIG_HOTPLUG_CPU)
    > + result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
    > + "crash/cpuhp",
    > + crash_cpuhp_online, crash_cpuhp_offline);
    > +#endif
    > +
    > + return result;
    > +}
    > +
    > +subsys_initcall(crash_hotplug_init);
    > +#endif /* CONFIG_CRASH_HOTPLUG */
    > --
    > 2.27.0
    >

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