linux-kernel - Re: [PATCH v21 2/7] crash: add generic infrastructure for crash hotplug support

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Message-ID: <ZC6nWzPuIWOxmvv2@MiWiFi-R3L-srv>
Date:   Thu, 6 Apr 2023 19:04:59 +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,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com
Subject: Re: [PATCH v21 2/7] crash: add generic infrastructure for crash
 hotplug support

On 04/04/23 at 02:03pm, Eric DeVolder wrote:
......
> +static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
> +{
> +	struct kimage *image;
> +
> +	/* Obtain lock while changing crash information */
> +	if (!kexec_trylock()) {
> +		pr_info("kexec_trylock() failed, elfcorehdr may be inaccurate\n");
> +		return;
> +	}
> +
> +	/* Check kdump is not loaded */
> +	if (!kexec_crash_image)
> +		goto out;
> +
> +	image = kexec_crash_image;
> +
> +	if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
> +		hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
> +		pr_debug("hp_action %u, cpu %u\n", hp_action, cpu);
> +	else
> +		pr_debug("hp_action %u\n", hp_action);

Seems we passed in the cpu number just for printing here. Wondering why
we don't print out hot added/removed memory ranges. Is the cpu number
printing necessary?

> +
> +	/*
> +	 * When the struct kimage is allocated, the elfcorehdr_index
> +	 * is set to -1. Find the segment containing the elfcorehdr,
> +	 * if not already found. This works for both the kexec_load
> +	 * and kexec_file_load paths.
> +	 */
> +	if (image->elfcorehdr_index < 0) {
> +		unsigned long mem;
> +		unsigned char *ptr;
> +		unsigned int n;
> +
> +		for (n = 0; n < image->nr_segments; n++) {
> +			mem = image->segment[n].mem;
> +			ptr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
> +			if (ptr) {
> +				/* The segment containing elfcorehdr */
> +				if (memcmp(ptr, ELFMAG, SELFMAG) == 0)
> +					image->elfcorehdr_index = (int)n;
> +				kunmap_local(ptr);
> +			}
> +		}
> +	}
> +
> +	if (image->elfcorehdr_index < 0) {
> +		pr_err("unable to locate elfcorehdr segment");
> +		goto out;
> +	}
> +
> +	/* Needed in order for the segments to be updated */
> +	arch_kexec_unprotect_crashkres();
> +
> +	/* Differentiate between normal load and hotplug update */
> +	image->hp_action = hp_action;
> +
> +	/* Now invoke arch-specific update handler */
> +	arch_crash_handle_hotplug_event(image);
> +
> +	/* No longer handling a hotplug event */
> +	image->hp_action = KEXEC_CRASH_HP_NONE;
> +	image->elfcorehdr_updated = true;
> +
> +	/* Change back to read-only */
> +	arch_kexec_protect_crashkres();
> +
> +out:
> +	/* Release lock now that update complete */
> +	kexec_unlock();
> +}
> +
> +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
> +{
> +	switch (val) {
> +	case MEM_ONLINE:
> +		crash_handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY,
> +			KEXEC_CRASH_HP_INVALID_CPU);
> +		break;
> +
> +	case MEM_OFFLINE:
> +		crash_handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY,
> +			KEXEC_CRASH_HP_INVALID_CPU);
> +		break;
> +	}
> +	return NOTIFY_OK;
> +}
> +
> +static struct notifier_block crash_memhp_nb = {
> +	.notifier_call = crash_memhp_notifier,
> +	.priority = 0
> +};
> +
> +static int crash_cpuhp_online(unsigned int cpu)
> +{
> +	crash_handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
> +	return 0;
> +}
> +
> +static int crash_cpuhp_offline(unsigned int cpu)
> +{
> +	crash_handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
> +	return 0;
> +}
> +
> +static int __init crash_hotplug_init(void)
> +{
> +	int result = 0;
> +
> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> +		register_memory_notifier(&crash_memhp_nb);
> +
> +	if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
> +		result = cpuhp_setup_state_nocalls(CPUHP_BP_PREPARE_DYN,
> +			"crash/cpuhp", crash_cpuhp_online, crash_cpuhp_offline);
> +	}
> +
> +	return result;
> +}
> +
> +subsys_initcall(crash_hotplug_init);
> +#endif
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 3d578c6fefee..8296d019737c 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -277,6 +277,12 @@ struct kimage *do_kimage_alloc_init(void)
>  	/* Initialize the list of unusable pages */
>  	INIT_LIST_HEAD(&image->unusable_pages);
>  
> +#ifdef CONFIG_CRASH_HOTPLUG
> +	image->hp_action = KEXEC_CRASH_HP_NONE;
> +	image->elfcorehdr_index = -1;
> +	image->elfcorehdr_updated = false;
> +#endif
> +
>  	return image;
>  }
>  
> -- 
> 2.31.1
>