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Date: Thu, 24 Mar 2022 21:49:11 +0800
From: Baoquan He <bhe@...hat.com>
To: Eric DeVolder <eric.devolder@...cle.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
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().
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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