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Date: Tue, 14 Mar 2023 18:43:24 +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 v19 2/7] crash: add generic infrastructure for crash
hotplug support
On 03/06/23 at 11:22am, Eric DeVolder wrote:
......
> +#ifdef CONFIG_CRASH_HOTPLUG
> +#undef pr_fmt
> +#define pr_fmt(fmt) "crash hp: " fmt
> +/*
> + * To accurately reflect hot un/plug changes of cpu and memory resources
> + * (including onling and offlining of those resources), the elfcorehdr
> + * (which is passed to the crash kernel via the elfcorehdr= parameter)
> + * must be updated with the new list of CPUs and memories.
> + *
> + * In order to make changes to elfcorehdr, two conditions are needed:
> + * First, the segment containing the elfcorehdr must be large enough
> + * to permit a growing number of resources; the elfcorehdr memory size
> + * is based on NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES.
> + * Second, purgatory must explicitly exclude the elfcorehdr from the
> + * list of segments it checks (since the elfcorehdr changes and thus
> + * would require an update to purgatory itself to update the digest).
> + */
> +static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
> +{
> + /* Obtain lock while changing crash information */
> + if (kexec_trylock()) {
> +
> + /* Check kdump is loaded */
> + if (kexec_crash_image) {
If the above check failed, I would directly return or jump out becuase
one indentation can be reduced.
> + struct kimage *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);
> +
> + /*
> + * 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
> +};
> +
Because for_each_possible_cpu() is taken in
crash_prepare_elf64_headers(), x86 doesn't need to respond to cpu
hotplug or doesn't do anything with this patchset. This cpu part in
infrastructure is only for the later powerpc usage, right?
> +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 969e8f52f7da..f2f9d41ce5df 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -276,6 +276,11 @@ struct kimage *do_kimage_alloc_init(void)
> /* Initialize the list of unusable pages */
> INIT_LIST_HEAD(&image->unusable_pages);
>
> +#ifdef CONFIG_CRASH_HOTPLUG
> + image->elfcorehdr_index = -1;
> + image->elfcorehdr_updated = false;
> +#endif
> +
> return image;
> }
>
> --
> 2.31.1
>
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