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Message-ID: <6f3a6cbb-0ac4-f178-fc17-18f9594da319@linux.ibm.com>
Date: Tue, 26 Apr 2022 09:36:59 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: Eric DeVolder <eric.devolder@...cle.com>,
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 v7 4/8] crash: add generic infrastructure for crash
hotplug support
On 15/04/22 03:59, Eric DeVolder wrote:
> Hi Baoquan,
> Inline comments below.
> Thanks!
> eric
>
> On 4/13/22 21:45, Baoquan He wrote:
>> 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@...cle.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
>>
> Sourabh Jain's work with PPC uses REMOVE_CPU, REMOVE_MEMORY, and
> ADD_MEMORY.
> Do you still want to consolidate these?
On PowerPC different actions are needed for CPU add and memory add/remove.
For CPU add case only FDT is updated whereas for the memory hotplug we
will be
updating FDT and elfcorehdr.
Ideally, I would prefer the crash hotplug handler to report all four
actions separately.
Thanks,
Sourabh Jain
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