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Tue, 15 Mar 2022 14:12:24 +0000 Message-ID: <2ca17bd8-fc81-19e2-7a16-e458ce8a097e@oracle.com> Date: Tue, 15 Mar 2022 09:12:17 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.1 Subject: Re: [PATCH v5 4/8] crash: generic crash hotplug support infrastructure Content-Language: en-US To: Sourabh Jain , linux-kernel@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, ebiederm@xmission.com, dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com, robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com References: <20220303162725.49640-1-eric.devolder@oracle.com> <20220303162725.49640-5-eric.devolder@oracle.com> <1b7405e4-e6a3-56ff-5068-d598ba2f2b5e@linux.ibm.com> From: Eric DeVolder In-Reply-To: <1b7405e4-e6a3-56ff-5068-d598ba2f2b5e@linux.ibm.com> Content-Type: text/plain; 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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 >> --- >>   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 Sourabh, I'm OK with that. Another idea might be if there are just two, and one of them is elfcorehdr, then perhaps in addition to elf_index and elf_index_valid, maybe we add an arch_index and arch_index_valid? In the case of PPC, the FDT would be stored in arch_index? Either way. Thanks! eric > > >> +#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 >>   #include >>   #include >> +#include >> +#include >> +#include >>   #include >>   #include >>   #include >> +#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 */