Messages in this thread | | | Date | Wed, 4 Jan 2023 10:20:38 -0600 | Subject | Re: [PATCH v15 7/7] x86/crash: add x86 crash hotplug support | From | Eric DeVolder <> |
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On 1/4/23 03:08, Baoquan He wrote: > On 12/09/22 at 10:36am, Eric DeVolder wrote: > ...... snip out >> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c >> index 9ceb93c176a6..5186df48ce6c 100644 >> --- a/arch/x86/kernel/crash.c >> +++ b/arch/x86/kernel/crash.c >> @@ -42,6 +42,21 @@ >> #include <asm/crash.h> >> #include <asm/cmdline.h> >> >> +/* >> + * For the kexec_file_load() syscall path, specify the maximum number of >> + * memory regions that the elfcorehdr buffer/segment can accommodate. >> + * These regions are obtained via walk_system_ram_res(); eg. the >> + * 'System RAM' entries in /proc/iomem. >> + * This value is combined with NR_CPUS_DEFAULT and multiplied by >> + * sizeof(Elf64_Phdr) to determine the final elfcorehdr memory buffer/ >> + * segment size. >> + * The value 8192, for example, covers a (sparsely populated) 1TiB system >> + * consisting of 128MiB memblocks, while resulting in an elfcorehdr >> + * memory buffer/segment size under 1MiB. This represents a sane choice >> + * to accommodate both baremetal and virtual machine configurations. >> + */ >> +#define CRASH_MAX_MEMORY_RANGES 8192 >> + >> /* Used while preparing memory map entries for second kernel */ >> struct crash_memmap_data { >> struct boot_params *params; >> @@ -394,10 +409,39 @@ int crash_load_segments(struct kimage *image) >> if (ret) >> return ret; >> >> - image->elf_headers = kbuf.buffer; >> - image->elf_headers_sz = kbuf.bufsz; >> + image->elf_headers = kbuf.buffer; >> + image->elf_headers_sz = kbuf.bufsz; >> + kbuf.memsz = kbuf.bufsz; >> + >> +#ifdef CONFIG_CRASH_HOTPLUG >> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) { > > Do I miss anything important during reviewing? I can't see why memory > hotplug is also relying on HOTPLUG_CPU.
No, looks like I made a mistake. The ifdef needs to go, and the IS_ENABLED() immediately following needs to be CRASH_HOTPLUG. Having not looked at this in a few weeks, it's obvious now. Thanks! eric
> >> + /* >> + * Ensure the elfcorehdr segment large enough for hotplug changes. >> + * Start with VMCOREINFO and kernel_map. >> + */ >> + unsigned long pnum = 2; >> + >> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) >> + pnum += CONFIG_NR_CPUS_DEFAULT; >> + >> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) >> + pnum += CRASH_MAX_MEMORY_RANGES; >> + >> + if (pnum < (unsigned long)PN_XNUM) { >> + kbuf.memsz = pnum * sizeof(Elf64_Phdr); >> + kbuf.memsz += sizeof(Elf64_Ehdr); >> + >> + image->elfcorehdr_index = image->nr_segments; >> + image->elfcorehdr_index_valid = true; >> + >> + /* Mark as usable to crash kernel, else crash kernel fails on boot */ >> + image->elf_headers_sz = kbuf.memsz; >> + } else { >> + pr_err("number of Phdrs %lu exceeds max\n", pnum); >> + } >> + } >> +#endif >> >> - kbuf.memsz = kbuf.bufsz; >> kbuf.buf_align = ELF_CORE_HEADER_ALIGN; >> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN; >> ret = kexec_add_buffer(&kbuf); >> @@ -412,3 +456,67 @@ int crash_load_segments(struct kimage *image) >> return ret; >> } >> #endif /* CONFIG_KEXEC_FILE */ >> + >> +#ifdef CONFIG_CRASH_HOTPLUG >> + >> +#undef pr_fmt >> +#define pr_fmt(fmt) "crash hp: " fmt >> + >> +/** >> + * arch_crash_handle_hotplug_event() - Handle hotplug elfcorehdr changes >> + * @image: the active struct kimage >> + * >> + * 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) >> +{ >> + void *elfbuf = NULL, *old_elfcorehdr; >> + unsigned long mem, memsz; >> + unsigned long elfsz = 0; >> + >> + /* >> + * Create the new elfcorehdr reflecting the changes to CPU and/or >> + * memory resources. >> + */ >> + if (prepare_elf_headers(image, &elfbuf, &elfsz)) { >> + pr_err("unable to prepare elfcore headers"); >> + goto out; >> + } >> + >> + /* >> + * Obtain address and size of the elfcorehdr segment, and >> + * check it against the new elfcorehdr buffer. >> + */ >> + mem = image->segment[image->elfcorehdr_index].mem; >> + memsz = image->segment[image->elfcorehdr_index].memsz; >> + if (elfsz > memsz) { >> + pr_err("update elfcorehdr elfsz %lu > memsz %lu", >> + elfsz, memsz); >> + goto out; >> + } >> + >> + /* >> + * Copy new elfcorehdr over the old elfcorehdr at destination. >> + */ >> + old_elfcorehdr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT)); >> + if (old_elfcorehdr) { >> + pr_err("updating elfcorehdr failed\n"); >> + goto out; >> + } >> + >> + /* >> + * Temporarily invalidate the crash image while the >> + * elfcorehdr is updated. >> + */ >> + xchg(&kexec_crash_image, NULL); >> + memcpy_flushcache(old_elfcorehdr, elfbuf, elfsz); >> + xchg(&kexec_crash_image, image); >> + kunmap_local(old_elfcorehdr); >> + pr_debug("updated elfcorehdr\n"); >> + >> +out: >> + vfree(elfbuf); >> +} >> +#endif >> -- >> 2.31.1 >> >
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