Re: [PATCH v15 3/7] crash: add generic infrastructure for crash hotplug support

[Baoquan He]

On 12/09/22 at 10:36am, 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_lock is held.
> 
> Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>

This looks good to me, thx.

Acked-by: Baoquan He <bhe@xxxxxxxxxx>

> ---
>  include/linux/crash_core.h |   8 +++
>  include/linux/kexec.h      |  12 ++++
>  kernel/crash_core.c        | 138 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 158 insertions(+)
> 
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index de62a722431e..a270f8660538 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
> +#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 ebf46c3b8f8b..389444cb03cc 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
> +	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 +511,10 @@ 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_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..fcb642a03d7b 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 +615,138 @@ 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;
> +				unsigned char *ptr;
> +				unsigned int n;
> +
> +				for (n = 0; n < image->nr_segments; n++) {
> +					mem = image->segment[n].mem;
> +					ptr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
> +					if (ptr) {
> +						/* The segment containing elfcorehdr */
> +						if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
> +							image->elfcorehdr_index = (int)n;
> +							image->elfcorehdr_index_valid = true;
> +						}
> +						kunmap_local(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
>