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Message-ID: <f2dbd4fe-6201-b5c4-2725-dec9c3dbf13e@linux.ibm.com>
Date:   Thu, 28 Apr 2022 10:48:50 +0530
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Subject: Re: [PATCH v7 4/8] crash: add generic infrastructure for crash
 hotplug support
Content-Language: en-US
To:     Baoquan He <bhe@redhat.com>
Cc:     Eric DeVolder <eric.devolder@oracle.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, vgoyal@redhat.com, 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: <20220413164237.20845-1-eric.devolder@oracle.com>
 <20220413164237.20845-5-eric.devolder@oracle.com>
 <YleK3J/4HNuFioIh@MiWiFi-R3L-srv>
 <4eea2373-32f3-9960-cbec-21dc1a428807@oracle.com>
 <6f3a6cbb-0ac4-f178-fc17-18f9594da319@linux.ibm.com>
 <YmeBjrChOHsIYG3e@MiWiFi-R3L-srv>
From:   Sourabh Jain <sourabhjain@linux.ibm.com>
In-Reply-To: <YmeBjrChOHsIYG3e@MiWiFi-R3L-srv>
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Hi Baoquan,

On 26/04/22 10:52, Baoquan He wrote:
> On 04/26/22 at 09:36am, Sourabh Jain wrote:
>> 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@oracle.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.
> I don't understand. For elfcorehdr updating, we only need regenerate it.
> Do you update them different for memory add/remove?

We have different actions for cpu remove, CPU add and memory add/remove 
case.

CPU remove: no action
CPU add: update flattened device tree (FDT)
memory add/remove: update FDT and regenerate/update elfcorehdr

Since memory add/remove action is same we can have common hp_action for 
them.

>
> What I saw is the added action for memory hotplug is only for message
> printing. Is this really needed? And memory hotplug is even not
> supported. Please correct me if I missed anything.

I agree that currently memory hp_action is only used for printing 
warning message but
eventually we will be handling memory hotplug case as well.

> +       /* crash update on memory hotplug is not support yet */
> +       if (hp_action == KEXEC_CRASH_HP_REMOVE_MEMORY || hp_action == KEXEC_CRASH_HP_ADD_MEMORY) {
> +               pr_info_once("crash hp: crash update is not supported with memory hotplug\n");
> +               return;
> +       }

Thanks,
Sourabh Jain