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Message-ID: <20220110080456.GG2731@MiWiFi-R3L-srv>
Date: Mon, 10 Jan 2022 16:04:56 +0800
From: Baoquan He <bhe@...hat.com>
To: Eric DeVolder <eric.devolder@...cle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
kexec@...ts.infradead.org, ebiederm@...ssion.com,
dyoung@...hat.com, vgoyal@...hat.com, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
robh@...nel.org, efault@....de, rppt@...nel.org,
konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [RFC v2 0/6] crash: Kernel handling of CPU and memory hot un/plug
Hi Eric,
On 01/05/22 at 08:25am, Eric DeVolder wrote:
> 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.
Thanks for taking a try on that, and sorry for late response because of
somethings at hand.
I will review this v2 round. When applying them, I encountered some
conflict, could you please rebase these on the ltest 5.16 and send me
a tar ball privately, or a github branch is also welcome. Thanks in
advance.
Thanks
Baoquan
>
> 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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