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Date: Tue, 15 Mar 2022 17:38:45 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: Eric DeVolder <eric.devolder@...cle.com>,
linux-kernel@...r.kernel.org, x86@...nel.org,
kexec@...ts.infradead.org, ebiederm@...ssion.com,
dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com
Cc: 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,
konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v5 4/8] crash: generic crash hotplug support
infrastructure
Hello Eric,
On 03/03/22 21:57, Eric DeVolder wrote:
> This patch introduces a generic crash hot plug/unplug infrastructure
> for CPU and memory changes. Upon CPU and memory changes, a generic
> crash_hotplug_handler() obtains the appropriate lock, does some
> important house keeping and then dispatches the hot plug/unplug event
> to the architecture specific arch_crash_hotplug_handler(), and when
> that handler returns, the lock is released.
>
> This patch modifies crash_core.c to implement a subsys_initcall()
> function that installs handlers for hot plug/unplug events. If CPU
> hotplug is enabled, then cpuhp_setup_state() is invoked to register a
> handler for CPU changes. Similarly, if memory hotplug is enabled, then
> register_memory_notifier() is invoked to install a handler for memory
> changes. These handlers in turn invoke the common generic handler
> crash_hotplug_handler().
>
> On the CPU side, cpuhp_setup_state_nocalls() is invoked with parameter
> CPUHP_AP_ONLINE_DYN. While this works, when a CPU is being unplugged,
> the CPU still shows up in foreach_present_cpu() during the regeneration
> of the new CPU list, thus the need to explicitly check and exclude the
> soon-to-be offlined CPU in crash_prepare_elf64_headers().
>
> On the memory side, each un/plugged memory block passes through the
> handler. For example, if a 1GiB DIMM is hotplugged, that generate 8
> memory events, one for each 128MiB memblock.
>
> Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
> ---
> include/linux/kexec.h | 16 +++++++
> kernel/crash_core.c | 108 ++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 124 insertions(+)
>
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index d7b59248441b..b11d75a6b2bc 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -300,6 +300,13 @@ struct kimage {
>
> /* Information for loading purgatory */
> struct purgatory_info purgatory_info;
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> + bool hotplug_event;
> + int offlinecpu;
> + bool elf_index_valid;
> + int elf_index;
How about keeping an array to track all kexec segment index need to be
updated in
crash hotplug handler.
struct hp_segment {
name;
index;
is_valid;
}
It will be helpful if architecture need to updated multiple kexec
segments for a hotplug event.
For example, on PowerPC, we might need to update FDT and elfcorehdr on
memory hot plug/unplug.
Thanks,
Sourabh Jain
> +#endif
> #endif
>
> #ifdef CONFIG_IMA_KEXEC
> @@ -316,6 +323,15 @@ struct kimage {
> unsigned long elf_load_addr;
> };
>
> +#ifdef CONFIG_CRASH_HOTPLUG
> +void arch_crash_hotplug_handler(struct kimage *image,
> + unsigned int hp_action, unsigned long a, unsigned long b);
> +#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..76959d440f71 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 +496,106 @@ 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 long a, unsigned long b)
> +{
> + pr_warn("crash hp: %s not implemented", __func__);
> +}
> +
> +static void crash_hotplug_handler(unsigned int hp_action,
> + unsigned long a, unsigned long b)
> +{
> + /* 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, a %lu, b %lu", hp_action,
> + a, b);
> +
> + /* 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, a, b);
> +
> + /* 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;
> + unsigned long start, end;
> +
> + start = mhp->start_pfn << PAGE_SHIFT;
> + end = ((mhp->start_pfn + mhp->nr_pages) << PAGE_SHIFT) - 1;
> +
> + switch (val) {
> + case MEM_ONLINE:
> + crash_hotplug_handler(KEXEC_CRASH_HP_ADD_MEMORY,
> + start, end-start);
> + break;
> +
> + case MEM_OFFLINE:
> + crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_MEMORY,
> + start, end-start);
> + 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, 0);
> + return 0;
> +}
> +
> +static int crash_cpuhp_offline(unsigned int cpu)
> +{
> + crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_CPU, cpu, 0);
> + 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 */
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