Nudge... Fwiw, below is a working changeset to kexec userspace utility that allows the kexec_load path to work similarly to the kexec_file_load path of this RFC. With both the following userspace kexec patch and this RFC, both kexec_load and kexec_file_load work with changes due to hotplug *without* unloading-then-reloading the kdump/capture kernel. eric diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c index 9826f6d..06adb7e 100644 --- a/kexec/arch/i386/crashdump-x86.c +++ b/kexec/arch/i386/crashdump-x86.c @@ -48,6 +48,7 @@ #include <x86/x86-linux.h> extern struct arch_options_t arch_options; +extern unsigned long long hotplug_size; static int get_kernel_page_offset(struct kexec_info *UNUSED(info), struct crash_elf_info *elf_info) @@ -975,6 +976,13 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline, } else { memsz = bufsz; } + + /* If hotplug support enabled, use that size */ + if (hotplug_size) { + memsz = hotplug_size; + } + + info->elfcorehdr = elfcorehdr = add_buffer(info, tmp, bufsz, memsz, align, min_base, max_addr, -1); dbgprintf("Created elf header segment at 0x%lx\n", elfcorehdr); diff --git a/kexec/kexec.c b/kexec/kexec.c index f63b36b..9569d9a 100644 --- a/kexec/kexec.c +++ b/kexec/kexec.c @@ -58,6 +58,7 @@ unsigned long long mem_min = 0; unsigned long long mem_max = ULONG_MAX; +unsigned long long hotplug_size = 0; static unsigned long kexec_flags = 0; /* Flags for kexec file (fd) based syscall */ static unsigned long kexec_file_flags = 0; @@ -672,6 +673,12 @@ static void update_purgatory(struct kexec_info *info) if (info->segment[i].mem == (void *)info->rhdr.rel_addr) { continue; } + /* Don't include elfcorehdr in the checksum, if hotplug + * support enabled. + */ + if (hotplug_size && (info->segment[i].mem == (void *)info->elfcorehdr)) { + continue; + } sha256_update(&ctx, info->segment[i].buf, info->segment[i].bufsz); nullsz = info->segment[i].memsz - info->segment[i].bufsz; @@ -1504,6 +1511,17 @@ int main(int argc, char *argv[]) case OPT_PRINT_CKR_SIZE: print_crashkernel_region_size(); return 0; + case OPT_HOTPLUG_SIZE: + /* Reserved the specified size for hotplug growth */ + hotplug_size = strtoul(optarg, &endptr, 0); + if (*endptr) { + fprintf(stderr, + "Bad option value in --hotplug-size=%s\n", + optarg); + usage(); + return 1; + } + break; default: break; } diff --git a/kexec/kexec.h b/kexec/kexec.h index 595dd68..b30dda4 100644 --- a/kexec/kexec.h +++ b/kexec/kexec.h @@ -169,6 +169,7 @@ struct kexec_info { int command_line_len; int skip_checks; + unsigned long elfcorehdr; }; struct arch_map_entry { @@ -231,7 +232,8 @@ extern int file_types; #define OPT_PRINT_CKR_SIZE 262 #define OPT_LOAD_LIVE_UPDATE 263 #define OPT_EXEC_LIVE_UPDATE 264 -#define OPT_MAX 265 +#define OPT_HOTPLUG_SIZE 265 +#define OPT_MAX 266 #define KEXEC_OPTIONS \ { "help", 0, 0, OPT_HELP }, \ { "version", 0, 0, OPT_VERSION }, \ @@ -258,6 +260,7 @@ extern int file_types; { "debug", 0, 0, OPT_DEBUG }, \ { "status", 0, 0, OPT_STATUS }, \ { "print-ckr-size", 0, 0, OPT_PRINT_CKR_SIZE }, \ + { "hotplug-size", 2, 0, OPT_HOTPLUG_SIZE }, \ #define KEXEC_OPT_STR "h?vdfixyluet:pscaS" On 12/7/21 13:51, Eric DeVolder wrote:
When the kdump service is loaded, if a CPU or memory is hot un/plugged, the crash elfcorehdr (for x86), which describes the CPUs and memory in the system, must also be updated, else the resulting vmcore is inaccurate (eg. missing either CPU context or memory regions). The current solution utilizes udev to initiate an unload-then-reload of the kdump image (e. kernel, initrd, boot_params, puratory and elfcorehdr) by the userspace kexec utility. In previous posts I have outlined the significant performance problems related to offloading this activity to userspace. This patchset introduces a generic crash hot un/plug handler that registers with the CPU and memory notifiers. Upon CPU or memory changes, this generic handler is invoked and performs important housekeeping, for example obtaining the appropriate lock, and then invokes an architecture specific handler to do the appropriate updates. In the case of x86_64, the arch specific handler generates a new elfcorehdr, and overwrites the old one in memory. No involvement with userspace needed. To realize the benefits/test this patchset, one must make a couple of minor changes to userspace: - Disable the udev rule for updating kdump on hot un/plug changes Eg. on RHEL: rm -f /usr/lib/udev/rules.d/98-kexec.rules or other technique to neuter the rule. - Change to the kexec_file_load for loading the kdump kernel: Eg. on RHEL: in /usr/bin/kdumpctl, change to: standard_kexec_args="-p -d -s" which adds the -s to select kexec_file_load syscall. This patchset supports kexec_load with a modified kexec userspace utility, on which I am current working to provide separately. Regards, eric --- RFC v2: 7dec2021 - Acting upon Baoquan He suggestion of removing elfcorehdr from the purgatory list of segments, removed purgatory code from patchset, and it is signficiantly simpler now. RFC v1: 18nov2021 https://lkml.org/lkml/2021/11/18/845 - working patchset demonstrating kernel handling of hotplug updates to x86 elfcorehdr for kexec_file_load RFC: 14dec2020 https://lkml.org/lkml/2020/12/14/532 - proposed concept of allowing kernel to handle hotplug update of elfcorehdr --- Eric DeVolder (6): crash: fix minor typo/bug in debug message crash hp: Introduce CRASH_HOTPLUG configuration options crash hp: definitions and prototype changes crash hp: generic crash hotplug support infrastructure crash hp: kexec_file changes for crash hotplug support crash hp: Add x86 crash hotplug support arch/x86/Kconfig | 26 ++++++++ arch/x86/kernel/crash.c | 140 +++++++++++++++++++++++++++++++++++++++- include/linux/kexec.h | 21 +++++- kernel/crash_core.c | 118 +++++++++++++++++++++++++++++++++ kernel/kexec_file.c | 15 ++++- 5 files changed, 314 insertions(+), 6 deletions(-)
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