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Date: Fri, 7 Oct 2022 14:33:18 -0500
From: Eric DeVolder <eric.devolder@...cle.com>
To: Sourabh Jain <sourabhjain@...ux.ibm.com>,
linux-kernel@...r.kernel.org, x86@...nel.org,
kexec@...ts.infradead.org, ebiederm@...ssion.com,
dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com
Cc: 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 v12 7/7] x86/crash: Add x86 crash hotplug support
On 9/19/22 02:06, Sourabh Jain wrote:
>
> On 10/09/22 02:35, Eric DeVolder wrote:
>> For x86_64, when CPU or memory is hot un/plugged, the crash
>> elfcorehdr, which describes the CPUs and memory in the system,
>> must also be updated.
>>
>> When loading the crash kernel via kexec_load or kexec_file_load,
>> the elfcorehdr is identified at run time in
>> crash_core:handle_hotplug_event().
>>
>> To update the elfcorehdr for x86_64, a new elfcorehdr must be
>> generated from the available CPUs and memory. The new elfcorehdr
>> is prepared into a buffer, and then installed over the top of
>> the existing elfcorehdr.
>>
>> In the patch 'kexec: exclude elfcorehdr from the segment digest'
>> the need to update purgatory due to the change in elfcorehdr was
>> eliminated. As a result, no changes to purgatory or boot_params
>> (as the elfcorehdr= kernel command line parameter pointer
>> remains unchanged and correct) are needed, just elfcorehdr.
>>
>> To accommodate a growing number of resources via hotplug, the
>> elfcorehdr segment must be sufficiently large enough to accommodate
>> changes, see the CRASH_MAX_MEMORY_RANGES configure item.
>>
>> With this change, crash hotplug for kexec_file_load syscall
>> is supported. The kexec_load is also supported, but also
>> requires a corresponding change to userspace kexec-tools.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
>> Acked-by: Baoquan He <bhe@...hat.com>
>> ---
>> arch/x86/Kconfig | 11 ++++
>> arch/x86/include/asm/kexec.h | 20 +++++++
>> arch/x86/kernel/crash.c | 102 +++++++++++++++++++++++++++++++++++
>> 3 files changed, 133 insertions(+)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index f9920f1341c8..cdfc9b2fdf98 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -2056,6 +2056,17 @@ config CRASH_DUMP
>> (CONFIG_RELOCATABLE=y).
>> For more details see Documentation/admin-guide/kdump/kdump.rst
>> +config CRASH_MAX_MEMORY_RANGES
>> + depends on CRASH_DUMP && KEXEC_FILE && (HOTPLUG_CPU || MEMORY_HOTPLUG)
>> + int
>> + default 32768
>> + help
>> + For the kexec_file_load path, specify the maximum number of
>> + memory regions, eg. as represented by the 'System RAM' entries
>> + in /proc/iomem, that the elfcorehdr buffer/segment can accommodate.
>> + This value is combined with NR_CPUS and multiplied by Elf64_Phdr
>> + size to determine the final buffer size.
>> +
>> config KEXEC_JUMP
>> bool "kexec jump"
>> depends on KEXEC && HIBERNATION
>> diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
>> index a3760ca796aa..432073385b2d 100644
>> --- a/arch/x86/include/asm/kexec.h
>> +++ b/arch/x86/include/asm/kexec.h
>> @@ -212,6 +212,26 @@ typedef void crash_vmclear_fn(void);
>> extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
>> extern void kdump_nmi_shootdown_cpus(void);
>> +void *arch_map_crash_pages(unsigned long paddr, unsigned long size);
>> +#define arch_map_crash_pages arch_map_crash_pages
>> +
>> +void arch_unmap_crash_pages(void **ptr);
>> +#define arch_unmap_crash_pages arch_unmap_crash_pages
>> +
>> +void arch_crash_handle_hotplug_event(struct kimage *image,
>> + unsigned int hp_action);
>> +#define arch_crash_handle_hotplug_event arch_crash_handle_hotplug_event
>> +
>> +#ifdef CONFIG_HOTPLUG_CPU
>> +static inline int crash_hotplug_cpu_support(void) { return 1; }
>> +#define crash_hotplug_cpu_support crash_hotplug_cpu_support
>> +#endif
>> +
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> +static inline int crash_hotplug_memory_support(void) { return 1; }
>> +#define crash_hotplug_memory_support crash_hotplug_memory_support
>> +#endif
>> +
>> #endif /* __ASSEMBLY__ */
>> #endif /* _ASM_X86_KEXEC_H */
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 9ceb93c176a6..8fc7d678ac72 100644
>> --- a/arch/x86/kernel/crash.c
>> +++ b/arch/x86/kernel/crash.c
>> @@ -25,6 +25,7 @@
>> #include <linux/slab.h>
>> #include <linux/vmalloc.h>
>> #include <linux/memblock.h>
>> +#include <linux/highmem.h>
>> #include <asm/processor.h>
>> #include <asm/hardirq.h>
>> @@ -397,7 +398,18 @@ int crash_load_segments(struct kimage *image)
>> image->elf_headers = kbuf.buffer;
>> image->elf_headers_sz = kbuf.bufsz;
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> + /* Ensure elfcorehdr segment large enough for hotplug changes */
>> + kbuf.memsz =
>> + (CONFIG_NR_CPUS_DEFAULT + CONFIG_CRASH_MAX_MEMORY_RANGES) *
>> + sizeof(Elf64_Phdr);
>> + /* Mark as usable to crash kernel, else crash kernel fails on boot */
>> + image->elf_headers_sz = kbuf.memsz;
>> + image->elfcorehdr_index = image->nr_segments;
>> + image->elfcorehdr_index_valid = true;
>> +#else
>> kbuf.memsz = kbuf.bufsz;
>> +#endif
>> kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
>> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>> ret = kexec_add_buffer(&kbuf);
>> @@ -412,3 +424,93 @@ int crash_load_segments(struct kimage *image)
>> return ret;
>> }
>> #endif /* CONFIG_KEXEC_FILE */
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +/*
>> + * NOTE: The addresses and sizes passed to this routine have
>> + * already been fully aligned on page boundaries. There is no
>> + * need for massaging the address or size.
>> + */
>> +void *arch_map_crash_pages(unsigned long paddr, unsigned long size)
>> +{
>> + void *ptr = NULL;
>> +
>> + if (size > 0) {
>> + struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
>> +
>> + ptr = kmap_local_page(page);
>> + }
>> +
>> + return ptr;
>> +}
>> +
>> +void arch_unmap_crash_pages(void **ptr)
>> +{
>> + if (ptr) {
>> + if (*ptr)
>> + kunmap_local(*ptr);
>> + *ptr = NULL;
>> + }
>> +}
>> +
>> +/**
>> + * arch_crash_handle_hotplug_event() - Handle hotplug elfcorehdr changes
>> + * @image: the active struct kimage
>> + * @hp_action: the hot un/plug action being handled
>> + *
>> + * To accurately reflect hot un/plug changes, the new elfcorehdr
>> + * is prepared in a kernel buffer, and then it is written on top
>> + * of the existing/old elfcorehdr.
>> + */
>> +void arch_crash_handle_hotplug_event(struct kimage *image,
>> + unsigned int hp_action)
>> +{
>> + struct kexec_segment *ksegment;
>> + unsigned char *ptr = NULL;
>> + unsigned long elfsz = 0;
>> + void *elfbuf = NULL;
>> + unsigned long mem, memsz;
>> +
>> + /*
>> + * Elfcorehdr_index_valid checked in crash_core:handle_hotplug_event()
>> + */
>> + ksegment = &image->segment[image->elfcorehdr_index];
>> + mem = ksegment->mem;
>> + memsz = ksegment->memsz;
>> +
>> + /*
>> + * Create the new elfcorehdr reflecting the changes to CPU and/or
>> + * memory resources.
>> + */
>> + if (prepare_elf_headers(image, &elfbuf, &elfsz)) {
>> + pr_err("crash hp: unable to prepare elfcore headers");
>> + goto out;
>
> On PowerPC, while preparing the elf core header the memblock structure is used to prepare program
> header for memory regions of elfcorehdr. Since the above arch specific hotplug handler gets invoked
> when memory is marked offline (MEM_OFFLINE) which is before memblock structure gets updated so on
> PowerPC the above handler may not work for memory hotplug case.
>
> Just wondering which data structure is used to get the list of memory regions while preparing
> program header for memory regions of elfcorehdr on other architectures?
>
> Thanks,
> Sourabh Jain
I think your request to report the memory block address in comments of patch 3/7 "crash: add generic
infrastructure" cover this scenario now.
Thanks,
eric
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