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Date: Thu, 24 Mar 2022 08:53:34 -0500
From: Eric DeVolder <eric.devolder@...cle.com>
To: Baoquan He <bhe@...hat.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
kexec@...ts.infradead.org, ebiederm@...ssion.com,
dyoung@...hat.com, vgoyal@...hat.com, 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
Baoquan,
Thanks, I've offered a minor correction below.
eric
On 3/24/22 08:49, Baoquan He wrote:
> On 03/24/22 at 09:38pm, Baoquan He wrote:
>> On 03/03/22 at 11:27am, 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.
>>
>> I rewrite the log as below with my understanding. Hope it's simpler to
>> help people get what's going on here. Please consider to take if it's
>> OK to you or adjust based on this. The code looks good to me.
>>
> Made some tuning:
>
> crash: add generic infrastructure for crash hotplug support
>
> Upon CPU and memory changes, a generic crash_hotplug_handler() is added
> to dispatch the hot plug/unplug event to the architecture specific
> arch_crash_hotplug_handler(). During the process, kexec_mutex need be
> held.
>
> To support cpu hotplug, one callback pair are registered to capture
> KEXEC_CRASH_HP_ADD_CPU and KEXEC_CRASH_HP_REMOVE_CPU events via
> cpuhp_setup_state_nocalls().
s/KEXEC_CRASH_HP_ADD}REMOVE_CPU/CPUHP_AP_ONLINE_DYN/ as the KEXEC_CRASH are the
names I've introduced with this patch?
>
> To support memory hotplug, a notifier crash_memhp_nb is registered to
> memory_chain to watch MEM_ONLINE and MEM_OFFLINE events.
>
> These callbacks and notifier will call crash_hotplug_handler() to handle
> captured event when invoked.
>
>>
>>>
>>> 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;
>>> +#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 */
>>> --
>>> 2.27.0
>>>
>>
>
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