Messages in this thread | | | Date | Wed, 26 Jan 2022 11:32:12 -0600 | Subject | Re: [PATCH v3 6/6] crash hp: Add x86 crash hotplug support | From | Eric DeVolder <> |
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Baoquan, Thanks for looking at this! See inline response below. eric
On 1/26/22 03:12, Baoquan He wrote: > On 01/21/22 at 08:06am, Eric DeVolder wrote: > ...... >>>> arch/x86/kernel/crash.c | 138 +++++++++++++++++++++++++++++++++++++++- >>>> 1 file changed, 137 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c >>>> index 9730c88530fc..d185137b33d4 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> >>>> @@ -265,7 +266,8 @@ static int prepare_elf_headers(struct kimage *image, void **addr, >>>> goto out; >>>> /* By default prepare 64bit headers */ >>>> - ret = crash_prepare_elf64_headers(cmem, IS_ENABLED(CONFIG_X86_64), addr, sz); >>>> + ret = crash_prepare_elf64_headers(image, cmem, >>>> + IS_ENABLED(CONFIG_X86_64), addr, sz); >>>> out: >>>> vfree(cmem); >>>> @@ -397,7 +399,17 @@ int crash_load_segments(struct kimage *image) >>>> image->elf_headers = kbuf.buffer; >>>> image->elf_headers_sz = kbuf.bufsz; >>>> +#ifdef CONFIG_CRASH_HOTPLUG >>>> + /* Ensure elfcorehdr segment large enough for hotplug changes */ >>>> + kbuf.memsz = CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ; >>> >>> I would define a default value for the size, meantime provide a Kconfig >>> option to allow user to customize. >> >> In patch 2/6 of this series, "crash hp: Introduce CRASH_HOTPLUG >> configuration options", I provide the following: >> >> +config CRASH_HOTPLUG_ELFCOREHDR_SZ >> + depends on CRASH_HOTPLUG >> + int >> + default 131072 >> + help >> + Specify the maximum size of the elfcorehdr buffer/segment. >> >> which defines a default value of 128KiB, and can be overriden at configure time. >> >> Are you asking for a different technique? > > I thought to define a global variable, like > > /* Defaults to ahve 128K elfcorehdr buffer which contains 2048 entries.*/ > unsigned long crash_hotplug_elfcorehdr_size = 0x20000; > > Then initialize it in crash_hotplug_init() if CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ > is enabled. > > Seems using the config directly is also OK. Let's keep it and see if > other people have comment.
OK, I will leave alone for the time being.
> >> >>> >>>> + /* For marking as usable to crash kernel */ >>>> + image->elf_headers_sz = kbuf.memsz; >>>> + /* Record the index of the elfcorehdr segment */ >>>> + image->elf_index = image->nr_segments; >>>> + image->elf_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 +424,127 @@ int crash_load_segments(struct kimage *image) >>>> return ret; >>>> } >>>> #endif /* CONFIG_KEXEC_FILE */ >>>> + >>>> +#ifdef CONFIG_CRASH_HOTPLUG >>> >>> These two helper function should be carved out into a separate patch as >>> a preparatory one. I am considering how to rearrange and split the >>> patches, will reply to cover letter. >> >> OK, I look forward to that insight! >> >>> >>>> +void *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 unmap_crash_pages(void **ptr) >>>> +{ >>>> + if (ptr) { >>>> + if (*ptr) >>>> + kunmap(*ptr); >>>> + *ptr = NULL; >>>> + } >>>> +} >>>> + >>>> +void arch_crash_hotplug_handler(struct kimage *image, >>>> + unsigned int hp_action, unsigned long a, unsigned long b) >>>> +{ >>>> + /* >>>> + * To accurately reflect hot un/plug changes, the elfcorehdr (which >>>> + * is passed to the crash kernel via the elfcorehdr= parameter) >>>> + * must be updated with the new list of CPUs and memories. The new >>>> + * elfcorehdr is prepared in a kernel buffer, and if no errors, >>>> + * then it is written on top of the existing/old elfcorehdr. >>>> + * >>>> + * Due to the change to the elfcorehdr, purgatory must explicitly >>>> + * exclude the elfcorehdr from the list of segments it checks. >>>> + */ >>> >>> Please move this code comment to above function as kernel-doc if you >>> this it benefits the entire function. Otherwise should move them above >>> the code block they are explaining. For this place, I think moving them >>> to above arch_crash_hotplug_handler() is better. >> >> ok, I will do that! >> >>> >>>> + struct kexec_segment *ksegment; >>>> + unsigned char *ptr = NULL; >>>> + unsigned long elfsz = 0; >>>> + void *elfbuf = NULL; >>>> + unsigned long mem, memsz; >>>> + unsigned int n; >>>> + >>>> + /* >>>> + * When the struct kimage is alloced, it is wiped to zero, so >>>> + * the elf_index_valid defaults to false. It is set on the >>>> + * kexec_file_load path, or here for kexec_load. >>>> + */ >>> >>> I think this kexec loading part should be taken out and post after this >>> whole patchset being accepted. At least, it's worth to put them in a >>> separate patch. >> >> This little bit of code that identifies the incoming elfcorehdr is all that >> is needed to support kexec_load (and the userspace changes of course). I'm >> happy to split as a separate patch, but I would think that be maintaining it >> with this series, then when it is accepted, both the kexec_load and >> kexec_file_load paths would be supported? Your call. > > Hmm, at first, let's split it out from this patch since it's an > independent action to kdump. I would suggest we don't carry it in this > series. After this series is done, you can post another patchset > including this part as kernel patch, and also the code change in > kexec_tools as user space patch. > > ...... >
OK, I'll remove the bit of code that supports kexec_load, so it can be introduced later coincident with the changes to kexec-tools.
In a previous message you mentioned making changes to the order of the patches, was this it, or is there more to come?
Thanks! eric
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