Messages in this thread | | | Date | Tue, 12 Jul 2022 15:31:11 -0500 | Subject | Re: [PATCH v9 7/7] x86/crash: Add x86 crash hotplug support | From | Eric DeVolder <> |
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On 7/11/22 04:57, Baoquan He wrote: > On 07/07/22 at 07:55am, Eric DeVolder wrote: >> >> >> On 6/20/22 00:06, Sourabh Jain wrote: >>> Hello Eric, >>> >>> On 14/06/22 04:12, 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@oracle.com> >>>> --- >>>> arch/x86/Kconfig | 11 ++++ >>>> arch/x86/kernel/crash.c | 116 ++++++++++++++++++++++++++++++++++++++++ >>>> 2 files changed, 127 insertions(+) >>>> >>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >>>> index 762a0b6ab8b6..e9eecff3b97d 100644 >>>> --- a/arch/x86/Kconfig >>>> +++ b/arch/x86/Kconfig >>>> @@ -2082,6 +2082,17 @@ 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/kernel/crash.c b/arch/x86/kernel/crash.c >>>> index 9db41cce8d97..b9cdf7a0d868 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> >>>> @@ -398,7 +399,17 @@ 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); >>>> + /* For marking as usable to crash kernel */ >>>> + image->elf_headers_sz = kbuf.memsz; >>>> + /* Record the index of the elfcorehdr segment */ >>>> + 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); >>>> @@ -413,3 +424,108 @@ int crash_load_segments(struct kimage *image) >>>> return ret; >>>> } >>>> #endif /* CONFIG_KEXEC_FILE */ >>>> + >>>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG) >>>> +int crash_hotplug_support(void) { return 1; } >>>> +void *arch_map_crash_pages(unsigned long paddr, unsigned long size) >>>> +{ >>>> + /* >>>> + * 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 *ptr = NULL; >>>> + >>>> + /* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */ >>>> + if (size > 0) { >>>> + struct page *page = pfn_to_page(paddr >> PAGE_SHIFT); >>>> + >>>> + ptr = kmap(page); >>>> + } >>>> + >>>> + return ptr; >>>> +} >>>> + >>>> +void arch_unmap_crash_pages(void **ptr) >>>> +{ >>>> + if (ptr) { >>>> + if (*ptr) >>>> + kunmap(*ptr); >>>> + *ptr = NULL; >>>> + } >>>> +} >>> >>> Aren't arch will have build issue if arch_[un]map_crash_pages methods are not defined? >> Sourabh, >> Yes, you are correct. I'll add __weak versions of each in crash_core.c in the next patch. > > Just a reminder, __weak is deprecated and has been cleaned up in > kernel/kexec*.c in below patch. > > [PATCH 0/2] kexec: Drop __weak attributes from functions > Baoquan, Thanks for the pointer! I have corrected this code to do away with __weak and use the style presented in the kexec patch. Eric
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