Messages in this thread | | | Date | Mon, 26 Sep 2022 14:19:38 -0500 | Subject | Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support | From | Eric DeVolder <> |
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Boris, I've a few questions for you below. With your responses, I am hopeful we can finish this series soon! Thanks, eric
On 9/13/22 14:12, Eric DeVolder wrote: > Boris, > Thanks for the feedback! Inline responses below. > eric > > On 9/12/22 01:52, Borislav Petkov wrote: >> On Fri, Sep 09, 2022 at 05:05:09PM -0400, 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, >> >> Please end function names with parentheses. Check the whole patch pls. > Done. > >> >>> 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. >> >> Redundant sentence. > Removed. > >> >>> The kexec_load is also supported, but also >>> requires a corresponding change to userspace kexec-tools. >> >> Ditto. > Removed. > >> >>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com> >>> Acked-by: Baoquan He <bhe@redhat.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. >> >> If I'm purely a user, I'm left wondering how to determine what to >> specify. Do you have a guidance text somewhere you can point to from >> here? > > This topic was discussed previously https://lkml.org/lkml/2022/3/3/372. > David points out that terminology is tricky here due to differing behaviors. > And perhaps that is your point in asking for guidance text. It can be > complicated, but it all comes down to System RAM entries. > > I could perhaps offer an overly simplified example such that for 1GiB block > size, for example, the CRASH_MAX_MEMORY_RANGES of 32768 would allow for 32TiB > of memory? > >> >>> + >>> 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); >> >> >> kbuf.memsz = CONFIG_NR_CPUS_DEFAULT + CONFIG_CRASH_MAX_MEMORY_RANGES; >> kbuf.memsz *= sizeof(Elf64_Phdr); >> >> looks more readable to me. > Done. > >> >> >>> + /* 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; >> >> Do that initialization at the top where you declare kbuf and get rid of >> the #else branch. > The kbuf.bufsz value is obtained via a call to prepare_elf_headers(); I can not initialize it at its > declaration. > >> >>> +#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) >> >> This ugly ifdeffery is still here. Why don't you have stubs for the >> !defined() cases in the header so that you can drop those here? >> > > I'm at a loss as to what to do differently here. You've raised this issue before and I went back and > looked at the suggestions then and I don't see how that applies to this situation. How is this > situation different than the #ifdef CONFIG_KEXEC_FILE that immediately preceeds it? > > I've included a copy of the current state of this section below for additional markup. > >>> +/* >>> + * 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; >>> +} >> >> if (size > 0) >> return kmap_local_page(pfn_to_page(paddr >> PAGE_SHIFT)); >> else >> return NULL; >> >> That's it. > Done. > >> >>> + >>> +void arch_unmap_crash_pages(void **ptr) >>> +{ >>> + if (ptr) { >>> + if (*ptr) >>> + kunmap_local(*ptr); >>> + *ptr = NULL; >>> + } >> >> Oh wow, this is just nuts. Why does it have to pass in a pointer to >> pointer which you have to carefully check twice? And why is it a void >> **? > A long time ago this made sense, but it no longer makes sense. I've corrected this. > >> >> And why are those called arch_ if all I see is the x86 variants? Are >> there gonna be other arches? And even if, why can't the other arches do >> kmap_local_page() too? > Currently there is a concurrent effort for PPC support by Sourabh Jain, and in that effort > arch_map_crash_pages() is using __va(paddr). > > I do not know the nuances between kmap_local_page() and __va() to answer the question. > > If kmap_local_page() works for all archs, then I'm happy to drop these arch_ variants > and use it directly. > >> >>> +} >>> + >>> +/** >>> + * 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) >> >> Align arguments on the opening brace. > Done. > >> >>> +{ >>> + struct kexec_segment *ksegment; >>> + unsigned char *ptr = NULL; >>> + unsigned long elfsz = 0; >>> + void *elfbuf = NULL; >>> + unsigned long mem, memsz; >> >> Please sort function local variables declaration in a reverse christmas >> tree order: >> >> <type A> longest_variable_name; >> <type B> shorter_var_name; >> <type C> even_shorter; >> <type D> i; >> > Done. > >>> + >>> + /* >>> + * Elfcorehdr_index_valid checked in crash_core:handle_hotplug_event() >> >> Elfcorehdr_index_valid?? > Comment reworked. > > >> >>> + */ >>> + 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"); >> ^^^^^^^^ >> >> this thing is done with pr_fmt(). Grep the tree for examples. > Done, thanks for pointing that out. > >> >>> + goto out; >>> + } >> >> The three lines above reading ksegment need to be here, where the test >> is done. > Done. > >> >>> + if (elfsz > memsz) { >>> + pr_err("crash hp: update elfcorehdr elfsz %lu > memsz %lu", >>> + elfsz, memsz); >>> + goto out; >>> + } >>> + >>> + /* >>> + * At this point, we are all but assured of success. >> >> Who is "we"? >> > Comment reworked. > > > Here is a copy of the current state of this code, for determining how to address the question above. > > #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG) > > #undef pr_fmt > #define pr_fmt(fmt) "crash hp: " fmt > > /* > * 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) > { > if (size > 0) > return kmap_local_page(pfn_to_page(paddr >> PAGE_SHIFT)); > else > return NULL; > } > > void arch_unmap_crash_pages(void *ptr) > { > if (ptr) > kunmap_local(ptr); > } > > /** > * 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) > { > unsigned long mem, memsz; > unsigned long elfsz = 0; > void *elfbuf = NULL; > void *ptr; > > /* > * 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. > */ > ptr = arch_map_crash_pages(mem, memsz); > if (ptr) { > /* > * Temporarily invalidate the crash image while the > * elfcorehdr is updated. > */ > xchg(&kexec_crash_image, NULL); > memcpy_flushcache(ptr, elfbuf, elfsz); > xchg(&kexec_crash_image, image); > } > arch_unmap_crash_pages(ptr); > pr_debug("re-loaded elfcorehdr at 0x%lx\n", mem); > > out: > if (elfbuf) > vfree(elfbuf); > } > #endif >
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