Messages in this thread | | | Date | Mon, 20 Jun 2022 10:36:58 +0530 | Subject | Re: [PATCH v9 7/7] x86/crash: Add x86 crash hotplug support | From | Sourabh Jain <> |
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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?
Thanks, Sourabh Jain
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