When the kdump service is loaded, if a CPU or memory is hot
un/plugged, the crash elfcorehdr, 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 (eg. 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; thus no
involvement with userspace needed.
To realize the benefits/test this patchset, one must make a couple
of minor changes to userspace:
- Prevent udev from updating kdump crash kernel on hot un/plug changes.
Add the following as the first lines to the RHEL udev rule file
/usr/lib/udev/rules.d/98-kexec.rules:
# The kernel handles updates to crash elfcorehdr for cpu and memory changes
SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
These lines will cause cpu and memory hot un/plug events to be
skipped within this rule file, with this changset applied.
- 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 kernel patchset also supports kexec_load() with a modified kexec
userspace utility. A working changeset to the kexec userspace utility
is posted to the kexec-tools mailing list here:
http://lists.infradead.org/pipermail/kexec/2022-October/026032.html
To use the kexec-tools patch, apply, build and install kexec-tools,
then change the kdumpctl's standard_kexec_args to replace the -s with
--hotplug. The removal of -s reverts to the kexec_load syscall and
the addition of --hotplug invokes the changes put forth in the
kexec-tools patch.
Regards,
eric
---
v15: 9dec2022
- Rebased onto 6.1.0-rc8
- Replaced arch_un/map_crash_pages() with direct use of
kun/map_local_pages(), per Boris.
- Some x86 changes, per Boris.
v14: 16nov2022
https://lkml.org/lkml/2022/11/16/1645
- Rebased onto 6.1.0-rc5
- Introduced CRASH_HOTPLUG Kconfig item to better fine tune
compilation of feature components, per Boris.
- Removed hp_action parameter to arch_crash_handle_hotplug_event()
as it is unused.
v13: 31oct2022
https://lkml.org/lkml/2022/10/31/854
- Rebased onto 6.1.0-rc3, which means converting to use the new
kexec_trylock() away from mutex_lock(kexec_mutex).
- Moved arch_un/map_crash_pages() into kexec.h and default
implementation using k/unmap_local_pages().
- Changed more #ifdef's into IS_ENABLED()
- Changed CRASH_MAX_MEMORY_RANGES to 8192 from 32768, and it moved
into x86 crash.c as #define rather Kconfig item, per Boris.
- Check number of Phdrs against PN_XNUM, max possible.
v12: 9sep2022
https://lkml.org/lkml/2022/9/9/1358
- Rebased onto 6.0-rc4
- Addressed some minor formatting items, per Baoquan
v11: 26aug2022
https://lkml.org/lkml/2022/8/26/963
- Rebased onto 6.0-rc2
- Redid the rework of __weak to use asm/kexec.h, per Baoquan
- Reworked some comments and minor items, per Baoquan
v10: 21jul2022
https://lkml.org/lkml/2022/7/21/1007
- Rebased to 5.19.0-rc7
- Per Sourabh, corrected build issue with arch_un/map_crash_pages()
for architectures not supporting this feature.
- Per David Hildebrand, removed the WARN_ONCE() altogether.
- Per David Hansen, converted to use of kmap_local_page().
- Per Baoquan He, replaced use of __weak with the kexec technique.
v9: 13jun2022
https://lkml.org/lkml/2022/6/13/3382
- Rebased to 5.18.0
- Per Sourabh, moved crash_prepare_elf64_headers() into common
crash_core.c to avoid compile issues with kexec_load only path.
- Per David Hildebrand, replaced mutex_trylock() with mutex_lock().
- Changed the __weak arch_crash_handle_hotplug_event() to utilize
WARN_ONCE() instead of WARN(). Fix some formatting issues.
- Per Sourabh, introduced sysfs attribute crash_hotplug for memory
and CPUs; for use by userspace (udev) to determine if the kernel
performs crash hot un/plug support.
- Per Sourabh, moved the code detecting the elfcorehdr segment from
arch/x86 into crash_core:handle_hotplug_event() so both kexec_load
and kexec_file_load can benefit.
- Updated userspace kexec-tools kexec utility to reflect change to
using CRASH_MAX_MEMORY_RANGES and get_nr_cpus().
- Updated the new proposed udev rules to reflect using the sysfs
attributes crash_hotplug.
v8: 5may2022
https://lkml.org/lkml/2022/5/5/1133
- Per Borislav Petkov, eliminated CONFIG_CRASH_HOTPLUG in favor
of CONFIG_HOTPLUG_CPU || CONFIG_MEMORY_HOTPLUG, ie a new define
is not needed. Also use of IS_ENABLED() rather than #ifdef's.
Renamed crash_hotplug_handler() to handle_hotplug_event().
And other corrections.
- Per Baoquan, minimized the parameters to the arch_crash_
handle_hotplug_event() to hp_action and cpu.
- Introduce KEXEC_CRASH_HP_INVALID_CPU definition, per Baoquan.
- Per Sourabh Jain, renamed and repurposed CRASH_HOTPLUG_ELFCOREHDR_SZ
to CONFIG_CRASH_MAX_MEMORY_RANGES, mirroring kexec-tools change
by David Hildebrand. Folded this patch into the x86
kexec_file_load support patch.
v7: 13apr2022
https://lkml.org/lkml/2022/4/13/850
- Resolved parameter usage to crash_hotplug_handler(), per Baoquan.
v6: 1apr2022
https://lkml.org/lkml/2022/4/1/1203
- Reword commit messages and some comment cleanup per Baoquan.
- Changed elf_index to elfcorehdr_index for clarity.
- Minor code changes per Baoquan.
v5: 3mar2022
https://lkml.org/lkml/2022/3/3/674
- Reworded description of CRASH_HOTPLUG_ELFCOREHDR_SZ, per
David Hildenbrand.
- Refactored slightly a few patches per Baoquan recommendation.
v4: 9feb2022
https://lkml.org/lkml/2022/2/9/1406
- Refactored patches per Baoquan suggestsions.
- A few corrections, per Baoquan.
v3: 10jan2022
https://lkml.org/lkml/2022/1/10/1212
- Rebasing per Baoquan He request.
- Changed memory notifier per David Hildenbrand.
- Providing example kexec userspace change in cover letter.
RFC v2: 7dec2021
https://lkml.org/lkml/2021/12/7/1088
- 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 (7):
crash: move crash_prepare_elf64_headers()
crash: prototype change for crash_prepare_elf64_headers()
crash: add generic infrastructure for crash hotplug support
kexec: exclude elfcorehdr from the segment digest
kexec: exclude hot remove cpu from elfcorehdr notes
crash: memory and cpu hotplug sysfs attributes
x86/crash: add x86 crash hotplug support
.../admin-guide/mm/memory-hotplug.rst | 8 +
Documentation/core-api/cpu_hotplug.rst | 18 ++
arch/arm64/kernel/machine_kexec_file.c | 6 +-
arch/powerpc/kexec/file_load_64.c | 2 +-
arch/riscv/kernel/elf_kexec.c | 7 +-
arch/x86/Kconfig | 12 +
arch/x86/include/asm/kexec.h | 15 ++
arch/x86/kernel/crash.c | 116 +++++++-
drivers/base/cpu.c | 14 +
drivers/base/memory.c | 13 +
include/linux/crash_core.h | 8 +
include/linux/kexec.h | 27 +-
kernel/crash_core.c | 255 ++++++++++++++++++
kernel/kexec_file.c | 105 +-------
14 files changed, 494 insertions(+), 112 deletions(-)
--
2.31.1
When a crash kernel is loaded via the kexec_file_load() syscall, the
kernel places the various segments (ie crash kernel, crash initrd,
boot_params, elfcorehdr, purgatory, etc) in memory. For those
architectures that utilize purgatory, a hash digest of the segments
is calculated for integrity checking. This digest is embedded into
the purgatory image prior to placing purgatory in memory.
Since hotplug events cause changes to the elfcorehdr, purgatory
integrity checking fails (at crash time, and no kdump created).
As a result, this change explicitly excludes the elfcorehdr segment
from the list of segments used to create the digest. By doing so,
this permits changes to the elfcorehdr in response to hotplug events,
without having to also reload purgatory due to the change to the
digest.
Signed-off-by: Eric DeVolder <[email protected]>
Acked-by: Baoquan He <[email protected]>
---
kernel/kexec_file.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index f98d1742872b..cc976948f17e 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -723,6 +723,12 @@ static int kexec_calculate_store_digests(struct kimage *image)
for (j = i = 0; i < image->nr_segments; i++) {
struct kexec_segment *ksegment;
+#ifdef CONFIG_CRASH_HOTPLUG
+ /* Exclude elfcorehdr segment to allow future changes via hotplug */
+ if (image->elfcorehdr_index_valid && (j == image->elfcorehdr_index))
+ continue;
+#endif
+
ksegment = &image->segment[i];
/*
* Skip purgatory as it will be modified once we put digest
--
2.31.1
Due to use of CPUHP_AP_ONLINE_DYN, upon CPU unplug, the CPU is
still in the for_each_present_cpu() list when within the
handle_hotplug_event(). Thus the CPU must be explicitly excluded
when building the new list of CPUs.
This change identifies in handle_hotplug_event() the CPU to be
excluded, and the check for excluding the CPU in
crash_prepare_elf64_headers().
Signed-off-by: Eric DeVolder <[email protected]>
Acked-by: Baoquan He <[email protected]>
---
kernel/crash_core.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index fcb642a03d7b..189065afd04f 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -366,6 +366,13 @@ int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
/* Prepare one phdr of type PT_NOTE for each present CPU */
for_each_present_cpu(cpu) {
+#ifdef CONFIG_CRASH_HOTPLUG
+ if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
+ /* Skip the soon-to-be offlined cpu */
+ if (image->hotplug_event && (cpu == image->offlinecpu))
+ continue;
+ }
+#endif
phdr->p_type = PT_NOTE;
notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
phdr->p_offset = phdr->p_paddr = notes_addr;
@@ -683,6 +690,16 @@ static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
/* Flag to differentiate between normal load and hotplug */
image->hotplug_event = true;
+ /*
+ * Due to use of CPUHP_AP_ONLINE_DYN, upon unplug and during
+ * this callback, the CPU is still in the for_each_present_cpu()
+ * list. Must explicitly look to exclude this CPU when building
+ * new list.
+ */
+ image->offlinecpu =
+ (hp_action == KEXEC_CRASH_HP_REMOVE_CPU) ?
+ cpu : KEXEC_CRASH_HP_INVALID_CPU;
+
/* Now invoke arch-specific update handler */
arch_crash_handle_hotplug_event(image);
--
2.31.1
This introduces the crash_hotplug attribute for memory and CPUs
for use by userspace. This change directly facilitates the udev
rule for managing userspace re-loading of the crash kernel upon
hot un/plug changes.
For memory, this changeset introduces the crash_hotplug attribute
to the /sys/devices/system/memory directory. For example:
# udevadm info --attribute-walk /sys/devices/system/memory/memory81
looking at device '/devices/system/memory/memory81':
KERNEL=="memory81"
SUBSYSTEM=="memory"
DRIVER==""
ATTR{online}=="1"
ATTR{phys_device}=="0"
ATTR{phys_index}=="00000051"
ATTR{removable}=="1"
ATTR{state}=="online"
ATTR{valid_zones}=="Movable"
looking at parent device '/devices/system/memory':
KERNELS=="memory"
SUBSYSTEMS==""
DRIVERS==""
ATTRS{auto_online_blocks}=="offline"
ATTRS{block_size_bytes}=="8000000"
ATTRS{crash_hotplug}=="1"
For CPUs, this changeset introduces the crash_hotplug attribute
to the /sys/devices/system/cpu directory. For example:
# udevadm info --attribute-walk /sys/devices/system/cpu/cpu0
looking at device '/devices/system/cpu/cpu0':
KERNEL=="cpu0"
SUBSYSTEM=="cpu"
DRIVER=="processor"
ATTR{crash_notes}=="277c38600"
ATTR{crash_notes_size}=="368"
ATTR{online}=="1"
looking at parent device '/devices/system/cpu':
KERNELS=="cpu"
SUBSYSTEMS==""
DRIVERS==""
ATTRS{crash_hotplug}=="1"
ATTRS{isolated}==""
ATTRS{kernel_max}=="8191"
ATTRS{nohz_full}==" (null)"
ATTRS{offline}=="4-7"
ATTRS{online}=="0-3"
ATTRS{possible}=="0-7"
ATTRS{present}=="0-3"
With these sysfs attributes in place, it is possible to efficiently
instruct the udev rule to skip crash kernel reloading.
For example, the following is the proposed udev rule change for RHEL
system 98-kexec.rules (as the first lines of the rule file):
# The kernel handles updates to crash elfcorehdr for cpu and memory changes
SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
When examined in the context of 98-kexec.rules, the above change
tests if crash_hotplug is set, and if so, it skips the userspace
initiated unload-then-reload of the crash kernel.
Cpu and memory checks are separated in accordance with
CONFIG_HOTPLUG_CPU and CONFIG_MEMORY_HOTPLUG kernel config options.
If an architecture supports, for example, memory hotplug but not
CPU hotplug, then the /sys/devices/system/memory/crash_hotplug
attribute file is present, but the /sys/devices/system/cpu/crash_hotplug
attribute file will NOT be present. Thus the udev rule will skip
userspace processing of memory hot un/plug events, but the udev
rule will fail for CPU events, thus allowing userspace to process
cpu hot un/plug events (ie the unload-then-reload of the kdump
capture kernel).
Signed-off-by: Eric DeVolder <[email protected]>
Acked-by: Baoquan He <[email protected]>
---
.../admin-guide/mm/memory-hotplug.rst | 8 ++++++++
Documentation/core-api/cpu_hotplug.rst | 18 ++++++++++++++++++
drivers/base/cpu.c | 14 ++++++++++++++
drivers/base/memory.c | 13 +++++++++++++
include/linux/kexec.h | 8 ++++++++
5 files changed, 61 insertions(+)
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index a3c9e8ad8fa0..15fd1751a63c 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -293,6 +293,14 @@ The following files are currently defined:
Availability depends on the CONFIG_ARCH_MEMORY_PROBE
kernel configuration option.
``uevent`` read-write: generic udev file for device subsystems.
+``crash_hotplug`` read-only: when changes to the system memory map
+ occur due to hot un/plug of memory, this file contains
+ '1' if the kernel updates the kdump capture kernel memory
+ map itself (via elfcorehdr), or '0' if userspace must update
+ the kdump capture kernel memory map.
+
+ Availability depends on the CONFIG_MEMORY_HOTPLUG kernel
+ configuration option.
====================== =========================================================
.. note::
diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst
index f75778d37488..0c8dc3fe5f94 100644
--- a/Documentation/core-api/cpu_hotplug.rst
+++ b/Documentation/core-api/cpu_hotplug.rst
@@ -750,6 +750,24 @@ will receive all events. A script like::
can process the event further.
+When changes to the CPUs in the system occur, the sysfs file
+/sys/devices/system/cpu/crash_hotplug contains '1' if the kernel
+updates the kdump capture kernel list of CPUs itself (via elfcorehdr),
+or '0' if userspace must update the kdump capture kernel list of CPUs.
+
+The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration
+option.
+
+To skip userspace processing of CPU hot un/plug events for kdump
+(ie the unload-then-reload to obtain a current list of CPUs), this sysfs
+file can be used in a udev rule as follows:
+
+ SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
+
+For a cpu hot un/plug event, if the architecture supports kernel updates
+of the elfcorehdr (which contains the list of CPUs), then the rule skips
+the unload-then-reload of the kdump capture kernel.
+
Kernel Inline Documentations Reference
======================================
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 4c98849577d4..fedbf87f9d13 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -293,6 +293,17 @@ static ssize_t print_cpus_nohz_full(struct device *dev,
static DEVICE_ATTR(nohz_full, 0444, print_cpus_nohz_full, NULL);
#endif
+#ifdef CONFIG_HOTPLUG_CPU
+#include <linux/kexec.h>
+static ssize_t crash_hotplug_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ return sprintf(buf, "%d\n", crash_hotplug_cpu_support());
+}
+static DEVICE_ATTR_ADMIN_RO(crash_hotplug);
+#endif
+
static void cpu_device_release(struct device *dev)
{
/*
@@ -469,6 +480,9 @@ static struct attribute *cpu_root_attrs[] = {
#ifdef CONFIG_NO_HZ_FULL
&dev_attr_nohz_full.attr,
#endif
+#ifdef CONFIG_HOTPLUG_CPU
+ &dev_attr_crash_hotplug.attr,
+#endif
#ifdef CONFIG_GENERIC_CPU_AUTOPROBE
&dev_attr_modalias.attr,
#endif
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 9aa0da991cfb..226be3134ffe 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -483,6 +483,16 @@ static ssize_t auto_online_blocks_store(struct device *dev,
static DEVICE_ATTR_RW(auto_online_blocks);
+#ifdef CONFIG_MEMORY_HOTPLUG
+#include <linux/kexec.h>
+static ssize_t crash_hotplug_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%d\n", crash_hotplug_memory_support());
+}
+static DEVICE_ATTR_RO(crash_hotplug);
+#endif
+
/*
* Some architectures will have custom drivers to do this, and
* will not need to do it from userspace. The fake hot-add code
@@ -881,6 +891,9 @@ static struct attribute *memory_root_attrs[] = {
&dev_attr_block_size_bytes.attr,
&dev_attr_auto_online_blocks.attr,
+#ifdef CONFIG_MEMORY_HOTPLUG
+ &dev_attr_crash_hotplug.attr,
+#endif
NULL
};
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 389444cb03cc..4d096bc97597 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -515,6 +515,14 @@ static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) {
static inline void arch_crash_handle_hotplug_event(struct kimage *image) { }
#endif
+#ifndef crash_hotplug_cpu_support
+static inline int crash_hotplug_cpu_support(void) { return 0; }
+#endif
+
+#ifndef crash_hotplug_memory_support
+static inline int crash_hotplug_memory_support(void) { return 0; }
+#endif
+
#else /* !CONFIG_KEXEC_CORE */
struct pt_regs;
struct task_struct;
--
2.31.1
When CPU or memory is hot un/plugged, the crash elfcorehdr, which
describes the CPUs and memory in the system, must also be updated.
A new elfcorehdr is generated from the available CPUs and memory
into a buffer, and then installed over the top of the existing
elfcorehdr. The segment containing the elfcorehdr is identified
at run time in crash_core:handle_hotplug_event(), which works for
both the kexec_load() and kexec_file_load() syscalls.
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 description.
Signed-off-by: Eric DeVolder <[email protected]>
---
arch/x86/Kconfig | 12 ++++
arch/x86/include/asm/kexec.h | 15 +++++
arch/x86/kernel/crash.c | 114 ++++++++++++++++++++++++++++++++++-
3 files changed, 138 insertions(+), 3 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 67745ceab0db..d1990a83e8f0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2072,6 +2072,18 @@ config CRASH_DUMP
(CONFIG_RELOCATABLE=y).
For more details see Documentation/admin-guide/kdump/kdump.rst
+config CRASH_HOTPLUG
+ bool "Update the crash elfcorehdr on system configuration changes"
+ default n
+ depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG)
+ help
+ Enable direct update to the crash elfcorehdr (which contains
+ the list of CPUs and memory regions to be dumped upon a crash)
+ in response to hot plug/unplug of CPUs or memory. This is a much
+ more advanced approach than userspace attempting that.
+
+ If unsure, say Y.
+
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..1bc852ce347d 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -212,6 +212,21 @@ typedef void crash_vmclear_fn(void);
extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
extern void kdump_nmi_shootdown_cpus(void);
+#ifdef CONFIG_CRASH_HOTPLUG
+void arch_crash_handle_hotplug_event(struct kimage *image);
+#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
+
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_KEXEC_H */
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9ceb93c176a6..5186df48ce6c 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -42,6 +42,21 @@
#include <asm/crash.h>
#include <asm/cmdline.h>
+/*
+ * For the kexec_file_load() syscall path, specify the maximum number of
+ * memory regions that the elfcorehdr buffer/segment can accommodate.
+ * These regions are obtained via walk_system_ram_res(); eg. the
+ * 'System RAM' entries in /proc/iomem.
+ * This value is combined with NR_CPUS_DEFAULT and multiplied by
+ * sizeof(Elf64_Phdr) to determine the final elfcorehdr memory buffer/
+ * segment size.
+ * The value 8192, for example, covers a (sparsely populated) 1TiB system
+ * consisting of 128MiB memblocks, while resulting in an elfcorehdr
+ * memory buffer/segment size under 1MiB. This represents a sane choice
+ * to accommodate both baremetal and virtual machine configurations.
+ */
+#define CRASH_MAX_MEMORY_RANGES 8192
+
/* Used while preparing memory map entries for second kernel */
struct crash_memmap_data {
struct boot_params *params;
@@ -394,10 +409,39 @@ int crash_load_segments(struct kimage *image)
if (ret)
return ret;
- image->elf_headers = kbuf.buffer;
- image->elf_headers_sz = kbuf.bufsz;
+ image->elf_headers = kbuf.buffer;
+ image->elf_headers_sz = kbuf.bufsz;
+ kbuf.memsz = kbuf.bufsz;
+
+#ifdef CONFIG_CRASH_HOTPLUG
+ if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
+ /*
+ * Ensure the elfcorehdr segment large enough for hotplug changes.
+ * Start with VMCOREINFO and kernel_map.
+ */
+ unsigned long pnum = 2;
+
+ if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
+ pnum += CONFIG_NR_CPUS_DEFAULT;
+
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
+ pnum += CRASH_MAX_MEMORY_RANGES;
+
+ if (pnum < (unsigned long)PN_XNUM) {
+ kbuf.memsz = pnum * sizeof(Elf64_Phdr);
+ kbuf.memsz += sizeof(Elf64_Ehdr);
+
+ image->elfcorehdr_index = image->nr_segments;
+ image->elfcorehdr_index_valid = true;
+
+ /* Mark as usable to crash kernel, else crash kernel fails on boot */
+ image->elf_headers_sz = kbuf.memsz;
+ } else {
+ pr_err("number of Phdrs %lu exceeds max\n", pnum);
+ }
+ }
+#endif
- kbuf.memsz = kbuf.bufsz;
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
ret = kexec_add_buffer(&kbuf);
@@ -412,3 +456,67 @@ int crash_load_segments(struct kimage *image)
return ret;
}
#endif /* CONFIG_KEXEC_FILE */
+
+#ifdef CONFIG_CRASH_HOTPLUG
+
+#undef pr_fmt
+#define pr_fmt(fmt) "crash hp: " fmt
+
+/**
+ * arch_crash_handle_hotplug_event() - Handle hotplug elfcorehdr changes
+ * @image: the active struct kimage
+ *
+ * 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)
+{
+ void *elfbuf = NULL, *old_elfcorehdr;
+ unsigned long mem, memsz;
+ unsigned long elfsz = 0;
+
+ /*
+ * 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.
+ */
+ old_elfcorehdr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
+ if (old_elfcorehdr) {
+ pr_err("updating elfcorehdr failed\n");
+ goto out;
+ }
+
+ /*
+ * Temporarily invalidate the crash image while the
+ * elfcorehdr is updated.
+ */
+ xchg(&kexec_crash_image, NULL);
+ memcpy_flushcache(old_elfcorehdr, elfbuf, elfsz);
+ xchg(&kexec_crash_image, image);
+ kunmap_local(old_elfcorehdr);
+ pr_debug("updated elfcorehdr\n");
+
+out:
+ vfree(elfbuf);
+}
+#endif
--
2.31.1
On 12/09/22 at 10:36am, Eric DeVolder wrote:
...... snip out
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 9ceb93c176a6..5186df48ce6c 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -42,6 +42,21 @@
> #include <asm/crash.h>
> #include <asm/cmdline.h>
>
> +/*
> + * For the kexec_file_load() syscall path, specify the maximum number of
> + * memory regions that the elfcorehdr buffer/segment can accommodate.
> + * These regions are obtained via walk_system_ram_res(); eg. the
> + * 'System RAM' entries in /proc/iomem.
> + * This value is combined with NR_CPUS_DEFAULT and multiplied by
> + * sizeof(Elf64_Phdr) to determine the final elfcorehdr memory buffer/
> + * segment size.
> + * The value 8192, for example, covers a (sparsely populated) 1TiB system
> + * consisting of 128MiB memblocks, while resulting in an elfcorehdr
> + * memory buffer/segment size under 1MiB. This represents a sane choice
> + * to accommodate both baremetal and virtual machine configurations.
> + */
> +#define CRASH_MAX_MEMORY_RANGES 8192
> +
> /* Used while preparing memory map entries for second kernel */
> struct crash_memmap_data {
> struct boot_params *params;
> @@ -394,10 +409,39 @@ int crash_load_segments(struct kimage *image)
> if (ret)
> return ret;
>
> - image->elf_headers = kbuf.buffer;
> - image->elf_headers_sz = kbuf.bufsz;
> + image->elf_headers = kbuf.buffer;
> + image->elf_headers_sz = kbuf.bufsz;
> + kbuf.memsz = kbuf.bufsz;
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
Do I miss anything important during reviewing? I can't see why memory
hotplug is also relying on HOTPLUG_CPU.
> + /*
> + * Ensure the elfcorehdr segment large enough for hotplug changes.
> + * Start with VMCOREINFO and kernel_map.
> + */
> + unsigned long pnum = 2;
> +
> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
> + pnum += CONFIG_NR_CPUS_DEFAULT;
> +
> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> + pnum += CRASH_MAX_MEMORY_RANGES;
> +
> + if (pnum < (unsigned long)PN_XNUM) {
> + kbuf.memsz = pnum * sizeof(Elf64_Phdr);
> + kbuf.memsz += sizeof(Elf64_Ehdr);
> +
> + image->elfcorehdr_index = image->nr_segments;
> + image->elfcorehdr_index_valid = true;
> +
> + /* Mark as usable to crash kernel, else crash kernel fails on boot */
> + image->elf_headers_sz = kbuf.memsz;
> + } else {
> + pr_err("number of Phdrs %lu exceeds max\n", pnum);
> + }
> + }
> +#endif
>
> - kbuf.memsz = kbuf.bufsz;
> kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
> ret = kexec_add_buffer(&kbuf);
> @@ -412,3 +456,67 @@ int crash_load_segments(struct kimage *image)
> return ret;
> }
> #endif /* CONFIG_KEXEC_FILE */
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> +
> +#undef pr_fmt
> +#define pr_fmt(fmt) "crash hp: " fmt
> +
> +/**
> + * arch_crash_handle_hotplug_event() - Handle hotplug elfcorehdr changes
> + * @image: the active struct kimage
> + *
> + * 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)
> +{
> + void *elfbuf = NULL, *old_elfcorehdr;
> + unsigned long mem, memsz;
> + unsigned long elfsz = 0;
> +
> + /*
> + * 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.
> + */
> + old_elfcorehdr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
> + if (old_elfcorehdr) {
> + pr_err("updating elfcorehdr failed\n");
> + goto out;
> + }
> +
> + /*
> + * Temporarily invalidate the crash image while the
> + * elfcorehdr is updated.
> + */
> + xchg(&kexec_crash_image, NULL);
> + memcpy_flushcache(old_elfcorehdr, elfbuf, elfsz);
> + xchg(&kexec_crash_image, image);
> + kunmap_local(old_elfcorehdr);
> + pr_debug("updated elfcorehdr\n");
> +
> +out:
> + vfree(elfbuf);
> +}
> +#endif
> --
> 2.31.1
>
On 1/4/23 03:08, Baoquan He wrote:
> On 12/09/22 at 10:36am, Eric DeVolder wrote:
> ...... snip out
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 9ceb93c176a6..5186df48ce6c 100644
>> --- a/arch/x86/kernel/crash.c
>> +++ b/arch/x86/kernel/crash.c
>> @@ -42,6 +42,21 @@
>> #include <asm/crash.h>
>> #include <asm/cmdline.h>
>>
>> +/*
>> + * For the kexec_file_load() syscall path, specify the maximum number of
>> + * memory regions that the elfcorehdr buffer/segment can accommodate.
>> + * These regions are obtained via walk_system_ram_res(); eg. the
>> + * 'System RAM' entries in /proc/iomem.
>> + * This value is combined with NR_CPUS_DEFAULT and multiplied by
>> + * sizeof(Elf64_Phdr) to determine the final elfcorehdr memory buffer/
>> + * segment size.
>> + * The value 8192, for example, covers a (sparsely populated) 1TiB system
>> + * consisting of 128MiB memblocks, while resulting in an elfcorehdr
>> + * memory buffer/segment size under 1MiB. This represents a sane choice
>> + * to accommodate both baremetal and virtual machine configurations.
>> + */
>> +#define CRASH_MAX_MEMORY_RANGES 8192
>> +
>> /* Used while preparing memory map entries for second kernel */
>> struct crash_memmap_data {
>> struct boot_params *params;
>> @@ -394,10 +409,39 @@ int crash_load_segments(struct kimage *image)
>> if (ret)
>> return ret;
>>
>> - image->elf_headers = kbuf.buffer;
>> - image->elf_headers_sz = kbuf.bufsz;
>> + image->elf_headers = kbuf.buffer;
>> + image->elf_headers_sz = kbuf.bufsz;
>> + kbuf.memsz = kbuf.bufsz;
>> +
>> +#ifdef CONFIG_CRASH_HOTPLUG
>> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
>
> Do I miss anything important during reviewing? I can't see why memory
> hotplug is also relying on HOTPLUG_CPU.
No, looks like I made a mistake. The ifdef needs to go, and the IS_ENABLED() immediately following
needs to be CRASH_HOTPLUG. Having not looked at this in a few weeks, it's obvious now.
Thanks!
eric
>
>> + /*
>> + * Ensure the elfcorehdr segment large enough for hotplug changes.
>> + * Start with VMCOREINFO and kernel_map.
>> + */
>> + unsigned long pnum = 2;
>> +
>> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
>> + pnum += CONFIG_NR_CPUS_DEFAULT;
>> +
>> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>> + pnum += CRASH_MAX_MEMORY_RANGES;
>> +
>> + if (pnum < (unsigned long)PN_XNUM) {
>> + kbuf.memsz = pnum * sizeof(Elf64_Phdr);
>> + kbuf.memsz += sizeof(Elf64_Ehdr);
>> +
>> + image->elfcorehdr_index = image->nr_segments;
>> + image->elfcorehdr_index_valid = true;
>> +
>> + /* Mark as usable to crash kernel, else crash kernel fails on boot */
>> + image->elf_headers_sz = kbuf.memsz;
>> + } else {
>> + pr_err("number of Phdrs %lu exceeds max\n", pnum);
>> + }
>> + }
>> +#endif
>>
>> - kbuf.memsz = kbuf.bufsz;
>> kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
>> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>> ret = kexec_add_buffer(&kbuf);
>> @@ -412,3 +456,67 @@ int crash_load_segments(struct kimage *image)
>> return ret;
>> }
>> #endif /* CONFIG_KEXEC_FILE */
>> +
>> +#ifdef CONFIG_CRASH_HOTPLUG
>> +
>> +#undef pr_fmt
>> +#define pr_fmt(fmt) "crash hp: " fmt
>> +
>> +/**
>> + * arch_crash_handle_hotplug_event() - Handle hotplug elfcorehdr changes
>> + * @image: the active struct kimage
>> + *
>> + * 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)
>> +{
>> + void *elfbuf = NULL, *old_elfcorehdr;
>> + unsigned long mem, memsz;
>> + unsigned long elfsz = 0;
>> +
>> + /*
>> + * 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.
>> + */
>> + old_elfcorehdr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
>> + if (old_elfcorehdr) {
>> + pr_err("updating elfcorehdr failed\n");
>> + goto out;
>> + }
>> +
>> + /*
>> + * Temporarily invalidate the crash image while the
>> + * elfcorehdr is updated.
>> + */
>> + xchg(&kexec_crash_image, NULL);
>> + memcpy_flushcache(old_elfcorehdr, elfbuf, elfsz);
>> + xchg(&kexec_crash_image, image);
>> + kunmap_local(old_elfcorehdr);
>> + pr_debug("updated elfcorehdr\n");
>> +
>> +out:
>> + vfree(elfbuf);
>> +}
>> +#endif
>> --
>> 2.31.1
>>
>