On 21/03/2022, 09:04:17, Sourabh Jain wrote: > This patch series implements the crash hotplug handler on PowerPC introduced > by https://lkml.org/lkml/2022/3/3/674 patch series. Hi Sourabh, That's a great idea! > > The Problem: > ============ > Post hotplug/DLPAR events the capture kernel holds stale information about the > system. Dump collection with stale capture kernel might end up in dump capture > failure or an inaccurate dump collection. > > > Existing solution: > ================== > The existing solution to keep the capture kernel up-to-date is observe the > hotplug event via udev rule and trigger a full capture kernel reload post > hotplug event. > > Shortcomings: > ------------------------------------------------ > - Leaves a window where kernel crash might not lead to successful dump > collection. > - Reloading all kexec components for each hotplug is inefficient. Since only > one or two kexec components need to be updated due to hotplug event reloading > all kexec component is redundant. > - udev rules are prone to races if hotplug events are frequent. > > More about issues with an existing solution is posted here: > - https://lkml.org/lkml/2020/12/14/532 > - https://lists.ozlabs.org/pipermail/linuxppc-dev/2022-February/240254.html > > Proposed Solution: > ================== > Instead of reloading all kexec segments on hotplug event, this patch series > focuses on updating only the relevant kexec segment. Once the kexec > segments are loaded in the kernel reserved area then an arch-specific hotplug handler > will update the relevant kexec segment based on hotplug event type. > > As mentioned above this patch series implemented a PowerPC crash hotplug > handler for the CPU. The crash hotplug handler memory is in our TODO list. If I understand corrrectly, and based on the change in the patch 4/5, memory hotplug operations are ignored. Does this means that once this series is applied, the capture kenrel will not be able to work correctly on this hot plug/unplugged memory areas? Thanks, Laurent. > > A couple of minor changes are required to realize the benefit of the patch > series: > > - disalble the udev rule: > > comment out the below line in kdump udev rule file: > RHEL: /usr/lib/udev/rules.d/98-kexec.rules > # SUBSYSTEM=="cpu", ACTION=="online", GOTO="kdump_reload_cpu" > > - kexec tool needs to be updated with patch for kexec_load system call > to work (not needed if -s option is used during kexec panic load): > > --- > diff --git a/kexec/arch/ppc64/kexec-elf-ppc64.c b/kexec/arch/ppc64/kexec-elf-ppc64.c > index 695b8b0..1dc6490 100644 > --- a/kexec/arch/ppc64/kexec-elf-ppc64.c > +++ b/kexec/arch/ppc64/kexec-elf-ppc64.c > @@ -45,6 +45,29 @@ uint64_t initrd_base, initrd_size; > unsigned char reuse_initrd = 0; > const char *ramdisk; > > +#define MAX_CORE 256 > +#define PER_CORE_NODE_SIZE 1500 > + > +/** > + * get_crash_fdt_mem_sz() - calcuate mem size for crash kernel FDT > + * @fdt: pointer to crash kernel FDT > + * > + * Calculate the buffer space needed to add more CPU nodes in FDT after > + * capture kenrel load due to hot add events. > + * > + * Some assumption are made to calculate the additional buffer size needed > + * to accommodate future hot add CPUs to the crash FDT. The maximum core count > + * in the system would not go beyond MAX_CORE and memory needed to store per core > + * date in FDT is PER_CORE_NODE_SIZE. > + * > + * Certainly MAX_CORE count can be replaced with possible core count and > + * PER_CORE_NODE_SIZE to some standard value instead of randomly observed > + * core size value on Power9 LPAR. > + */ > +static unsigned int get_crash_fdt_mem_sz(void *fdt) { > + return fdt_totalsize(fdt) + (PER_CORE_NODE_SIZE * MAX_CORE); > +} > + > int elf_ppc64_probe(const char *buf, off_t len) > { > struct mem_ehdr ehdr; > @@ -179,6 +202,7 @@ int elf_ppc64_load(int argc, char **argv, const char *buf, off_t len, > uint64_t max_addr, hole_addr; > char *seg_buf = NULL; > off_t seg_size = 0; > + unsigned int mem_sz = 0; > struct mem_phdr *phdr; > size_t size; > #ifdef NEED_RESERVE_DTB > @@ -329,7 +353,13 @@ int elf_ppc64_load(int argc, char **argv, const char *buf, off_t len, > if (result < 0) > return result; > > - my_dt_offset = add_buffer(info, seg_buf, seg_size, seg_size, > + if (info->kexec_flags & KEXEC_ON_CRASH) { > + mem_sz = get_crash_fdt_mem_sz((void *)seg_buf); > + fdt_set_totalsize(seg_buf, mem_sz); > + info->fdt_index = info->nr_segments; > + } > + > + my_dt_offset = add_buffer(info, seg_buf, seg_size, mem_sz, > 0, 0, max_addr, -1); > > #ifdef NEED_RESERVE_DTB > diff --git a/kexec/kexec.c b/kexec/kexec.c > index f63b36b..846b1a8 100644 > --- a/kexec/kexec.c > +++ b/kexec/kexec.c > @@ -672,6 +672,9 @@ static void update_purgatory(struct kexec_info *info) > if (info->segment[i].mem == (void *)info->rhdr.rel_addr) { > continue; > } > + if (info->fdt_index == i) > + continue; > + > sha256_update(&ctx, info->segment[i].buf, > info->segment[i].bufsz); > nullsz = info->segment[i].memsz - info->segment[i].bufsz; > diff --git a/kexec/kexec.h b/kexec/kexec.h > index 595dd68..0906a1b 100644 > --- a/kexec/kexec.h > +++ b/kexec/kexec.h > @@ -169,6 +169,7 @@ struct kexec_info { > int command_line_len; > > int skip_checks; > + // Given that we might need to update mutliple kexec segments > + // then having array to keep indexes of all hotplug kexec segments > + // will be helpful. > + unsigned int fdt_index; > }; > > struct arch_map_entry { > --- > > --- > Changelog: > > v1 -> v2: > - Use generic hotplug handler introduced by https://lkml.org/lkml/2022/2/9/1406, a > significant change from v1. > > v2 -> v3 > - Move fdt_index and fdt_index_vaild variables to kimage_arch struct. > - Rebase patche on top of https://lkml.org/lkml/2022/3/3/674 [v5] > - Fixed warning reported by checpatch script > --- > > Sourabh Jain (5): > powerpc/kexec: make update_cpus_node non-static > powerpc/crash hp: introduce a new config option CRASH_HOTPLUG > powrepc/crash hp: update kimage struct > powerpc/crash hp: add crash hotplug support for kexec_file_load > powerpc/crash hp: add crash hotplug support for kexec_load > > arch/powerpc/Kconfig | 11 +++ > arch/powerpc/include/asm/kexec.h | 3 + > arch/powerpc/kexec/core_64.c | 153 ++++++++++++++++++++++++++++++ > arch/powerpc/kexec/elf_64.c | 40 ++++++++ > arch/powerpc/kexec/file_load_64.c | 87 ----------------- > 5 files changed, 207 insertions(+), 87 deletions(-) > _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
