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, and a working changeset to the kexec userspace utility
is provided here (and to use, the above change to standard_kexec_args
would be, for example, to append --hotplug-size=262144 instead of -s).
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"
Regards,
eric
---
v5: 3mar2022
- 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 (8):
x86/crash: fix minor typo/bug in debug message
x86/crash hp: Introduce CRASH_HOTPLUG configuration options
crash: prototype change for crash_prepare_elf64_headers
crash: generic crash hotplug support infrastructure
kexec: exclude elfcorehdr from the segment digest
kexec: exclude hot remove cpu from elfcorehdr notes
x86/crash: Add x86 crash hotplug support for kexec_file_load
x86/crash: Add x86 crash hotplug support for kexec_load
arch/arm64/kernel/machine_kexec_file.c | 6 +-
arch/powerpc/kexec/file_load_64.c | 2 +-
arch/x86/Kconfig | 26 +++++
arch/x86/kernel/crash.c | 151 ++++++++++++++++++++++++-
include/linux/kexec.h | 21 +++-
kernel/crash_core.c | 118 +++++++++++++++++++
kernel/kexec_file.c | 15 ++-
7 files changed, 329 insertions(+), 10 deletions(-)
--
2.27.0
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.
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 if no errors occur, it is
installed over the top of the existing elfcorehdr.
In the patch 'crash hp: 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_HOTPLUG_ELFCOREHDR_SZ configure item.
With this change, the kexec_file_load syscall (not kexec_load)
is supported. When loading the crash kernel via kexec_file_load,
the elfcorehdr is identified at load time in crash_load_segments().
Signed-off-by: Eric DeVolder <[email protected]>
---
arch/x86/kernel/crash.c | 120 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 120 insertions(+)
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9db41cce8d97..5da30e2bc780 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>
@@ -398,7 +399,17 @@ int crash_load_segments(struct kimage *image)
image->elf_headers = kbuf.buffer;
image->elf_headers_sz = kbuf.bufsz;
+#ifdef CONFIG_CRASH_HOTPLUG
+ /* Ensure elfcorehdr segment large enough for hotplug changes */
+ kbuf.memsz = CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ;
+ /* For marking as usable to crash kernel */
+ image->elf_headers_sz = kbuf.memsz;
+ /* Record the index of the elfcorehdr segment */
+ image->elf_index = image->nr_segments;
+ image->elf_index_valid = true;
+#else
kbuf.memsz = kbuf.bufsz;
+#endif
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
ret = kexec_add_buffer(&kbuf);
@@ -413,3 +424,112 @@ int crash_load_segments(struct kimage *image)
return ret;
}
#endif /* CONFIG_KEXEC_FILE */
+
+#ifdef CONFIG_CRASH_HOTPLUG
+static void *map_crash_pages(unsigned long paddr, unsigned long size)
+{
+ /*
+ * 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 *ptr = NULL;
+
+ /* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */
+ if (size > 0) {
+ struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
+
+ ptr = kmap(page);
+ }
+
+ return ptr;
+}
+
+static void unmap_crash_pages(void **ptr)
+{
+ if (ptr) {
+ if (*ptr)
+ kunmap(*ptr);
+ *ptr = NULL;
+ }
+}
+
+/**
+ * arch_crash_hotplug_handler() - Handle hotplug elfcorehdr changes
+ * @image: the active struct kimage
+ * @hp_action: the hot un/plug action being handled
+ * @a: first parameter dependent upon hp_action
+ * @b: first parameter dependent upon hp_action
+ *
+ * To accurately reflect hot un/plug changes, the elfcorehdr (which
+ * is passed to the crash kernel via the elfcorehdr= parameter)
+ * must be updated with the new list of CPUs and memories. The new
+ * elfcorehdr is prepared in a kernel buffer, and if no errors,
+ * then it is written on top of the existing/old elfcorehdr.
+ *
+ * For hotplug changes to elfcorehdr to work, two conditions are
+ * needed:
+ * First, the segment containing the elfcorehdr must be large enough
+ * to permit a growing number of resources. See
+ * CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ.
+ * Second, purgatory must explicitly exclude the elfcorehdr from the
+ * list of segments it checks (since the elfcorehdr changes and thus
+ * would require an update to purgatory itself to update the digest).
+ *
+ */
+void arch_crash_hotplug_handler(struct kimage *image,
+ unsigned int hp_action, unsigned long a, unsigned long b)
+{
+ struct kexec_segment *ksegment;
+ unsigned char *ptr = NULL;
+ unsigned long elfsz = 0;
+ void *elfbuf = NULL;
+ unsigned long mem, memsz;
+
+ /* Must have valid elfcorehdr index */
+ if (!image->elf_index_valid) {
+ pr_err("crash hp: unable to locate elfcorehdr segment");
+ goto out;
+ }
+
+ ksegment = &image->segment[image->elf_index];
+ mem = ksegment->mem;
+ memsz = ksegment->memsz;
+
+ /*
+ * Create the new elfcorehdr reflecting the changes to CPU and/or
+ * memory resources. The elfcorehdr segment memsz must be
+ * sufficiently large to accommodate increases due to hotplug
+ * activity. See CRASH_HOTPLUG_ELFCOREHDR_SZ.
+ */
+ if (prepare_elf_headers(image, &elfbuf, &elfsz)) {
+ pr_err("crash hp: unable to prepare elfcore headers");
+ goto out;
+ }
+ 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.
+ * Copy new elfcorehdr into destination.
+ */
+ ptr = map_crash_pages(mem, memsz);
+ if (ptr) {
+ /* Temporarily invalidate the crash image while it is replaced */
+ xchg(&kexec_crash_image, NULL);
+ /* Write the new elfcorehdr into memory */
+ memcpy_flushcache((void *)ptr, elfbuf, elfsz);
+ /* The crash image is now valid once again */
+ xchg(&kexec_crash_image, image);
+ }
+ unmap_crash_pages((void **)&ptr);
+ pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
+
+out:
+ if (elfbuf)
+ vfree(elfbuf);
+}
+#endif /* CONFIG_CRASH_HOTPLUG */
--
2.27.0
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
crash_hotplug_handler(). Thus the CPU must be explicitly excluded
when building the new list of CPUs.
This change identifies in crash_hotplug_handler() 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 | 10 ++++++++++
kernel/kexec_file.c | 5 +++++
2 files changed, 15 insertions(+)
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 76959d440f71..d3fd51f2195c 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -522,6 +522,16 @@ static void crash_hotplug_handler(unsigned int hp_action,
/* Flag to differentiate between normal load and hotplug */
kexec_crash_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.
+ */
+ kexec_crash_image->offlinecpu =
+ (hp_action == KEXEC_CRASH_HP_REMOVE_CPU) ?
+ (unsigned int)a : ~0U;
+
/* Now invoke arch-specific update handler */
arch_crash_hotplug_handler(kexec_crash_image, hp_action, a, b);
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 93bb0c0ce66c..339995d42169 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -1314,6 +1314,11 @@ 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
+ /* 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;
--
2.27.0
From within crash_prepare_elf64_headers() there is a need to
reference the struct kimage hotplug members. As such, this
change passes the struct kimage as a parameter to the
crash_prepare_elf64_headers().
This is preparation for later patch, no functionality change.
Signed-off-by: Eric DeVolder <[email protected]>
Acked-by: Baoquan He <[email protected]>
---
arch/arm64/kernel/machine_kexec_file.c | 6 +++---
arch/powerpc/kexec/file_load_64.c | 2 +-
arch/x86/kernel/crash.c | 3 ++-
include/linux/kexec.h | 5 +++--
kernel/kexec_file.c | 4 ++--
5 files changed, 11 insertions(+), 9 deletions(-)
diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
index 59c648d51848..7dbafb42ecf2 100644
--- a/arch/arm64/kernel/machine_kexec_file.c
+++ b/arch/arm64/kernel/machine_kexec_file.c
@@ -39,7 +39,7 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
return kexec_image_post_load_cleanup_default(image);
}
-static int prepare_elf_headers(void **addr, unsigned long *sz)
+static int prepare_elf_headers(struct kimage *image, void **addr, unsigned long *sz)
{
struct crash_mem *cmem;
unsigned int nr_ranges;
@@ -67,7 +67,7 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
if (!ret)
- ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
+ ret = crash_prepare_elf64_headers(image, cmem, true, addr, sz);
kfree(cmem);
return ret;
@@ -96,7 +96,7 @@ int load_other_segments(struct kimage *image,
/* load elf core header */
if (image->type == KEXEC_TYPE_CRASH) {
- ret = prepare_elf_headers(&headers, &headers_sz);
+ ret = prepare_elf_headers(image, &headers, &headers_sz);
if (ret) {
pr_err("Preparing elf core header failed\n");
goto out_err;
diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
index b4981b651d9a..07da6bf1cf24 100644
--- a/arch/powerpc/kexec/file_load_64.c
+++ b/arch/powerpc/kexec/file_load_64.c
@@ -797,7 +797,7 @@ static int load_elfcorehdr_segment(struct kimage *image, struct kexec_buf *kbuf)
goto out;
/* Setup elfcorehdr segment */
- ret = crash_prepare_elf64_headers(cmem, false, &headers, &headers_sz);
+ ret = crash_prepare_elf64_headers(image, cmem, false, &headers, &headers_sz);
if (ret) {
pr_err("Failed to prepare elf headers for the core\n");
goto out;
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 9730c88530fc..9db41cce8d97 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -265,7 +265,8 @@ static int prepare_elf_headers(struct kimage *image, void **addr,
goto out;
/* By default prepare 64bit headers */
- ret = crash_prepare_elf64_headers(cmem, IS_ENABLED(CONFIG_X86_64), addr, sz);
+ ret = crash_prepare_elf64_headers(image, cmem,
+ IS_ENABLED(CONFIG_X86_64), addr, sz);
out:
vfree(cmem);
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 0c994ae37729..d7b59248441b 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -221,8 +221,9 @@ struct crash_mem {
extern int crash_exclude_mem_range(struct crash_mem *mem,
unsigned long long mstart,
unsigned long long mend);
-extern int crash_prepare_elf64_headers(struct crash_mem *mem, int kernel_map,
- void **addr, unsigned long *sz);
+extern int crash_prepare_elf64_headers(struct kimage *image,
+ struct crash_mem *mem, int kernel_map,
+ void **addr, unsigned long *sz);
#endif /* CONFIG_KEXEC_FILE */
#ifdef CONFIG_KEXEC_ELF
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 8347fc158d2b..801d0d0a5012 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -1260,8 +1260,8 @@ int crash_exclude_mem_range(struct crash_mem *mem,
return 0;
}
-int crash_prepare_elf64_headers(struct crash_mem *mem, int kernel_map,
- void **addr, unsigned long *sz)
+int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
+ int kernel_map, void **addr, unsigned long *sz)
{
Elf64_Ehdr *ehdr;
Elf64_Phdr *phdr;
--
2.27.0
The pr_debug() intends to display the memsz member, but the
parameter is actually the bufsz member (which is already
displayed). Correct this to display memsz value.
Signed-off-by: Eric DeVolder <[email protected]>
Acked-by: Baoquan He <[email protected]>
---
arch/x86/kernel/crash.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index e8326a8d1c5d..9730c88530fc 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -407,7 +407,7 @@ int crash_load_segments(struct kimage *image)
}
image->elf_load_addr = kbuf.mem;
pr_debug("Loaded ELF headers at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
- image->elf_load_addr, kbuf.bufsz, kbuf.bufsz);
+ image->elf_load_addr, kbuf.bufsz, kbuf.memsz);
return ret;
}
--
2.27.0
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 801d0d0a5012..93bb0c0ce66c 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -765,6 +765,12 @@ 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
+ /* This segment excluded to allow future changes via hotplug */
+ if (image->elf_index_valid && (j == image->elf_index))
+ continue;
+#endif
+
ksegment = &image->segment[i];
/*
* Skip purgatory as it will be modified once we put digest
--
2.27.0
For kexec_file_load support, the loading of the crash kernel occurs
entirely within the kernel, and as such the elfcorehdr is readily
identified (so that it can be modified upon hotplug events).
This change enables support for kexec_load by identifying the
elfcorehdr segment in the arch_crash_hotplug_handler(), if it has
not already been identified.
In general, support for kexec_load requires corresponding changes
to the userspace kexec-tools utility. It is the responsibility of
the userspace kexec utility to ensure that:
- the elfcorehdr segment is sufficiently large enough to accommodate
hotplug changes, ala CRASH_HOTPLUG_ELFCOREHDR_SZ.
- provides a purgatory that excludes the elfcorehdr from its list of
run-time segments to check.
These changes to the userspace kexec utility are available, but not
yet accepted upstream.
Signed-off-by: Eric DeVolder <[email protected]>
---
arch/x86/kernel/crash.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 5da30e2bc780..45cc6e3af63e 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -486,6 +486,32 @@ void arch_crash_hotplug_handler(struct kimage *image,
void *elfbuf = NULL;
unsigned long mem, memsz;
+ /*
+ * When the struct kimage is alloced, it is wiped to zero, so
+ * the elf_index_valid defaults to false. It is set on the
+ * kexec_file_load path, or here for kexec_load.
+ */
+ if (!image->elf_index_valid) {
+ unsigned int n;
+
+ for (n = 0; n < image->nr_segments; n++) {
+ mem = image->segment[n].mem;
+ memsz = image->segment[n].memsz;
+ ptr = map_crash_pages(mem, memsz);
+ if (ptr) {
+ /* The segment containing elfcorehdr */
+ if ((ptr[0] == 0x7F) &&
+ (ptr[1] == 'E') &&
+ (ptr[2] == 'L') &&
+ (ptr[3] == 'F')) {
+ image->elf_index = (int)n;
+ image->elf_index_valid = true;
+ }
+ }
+ unmap_crash_pages((void **)&ptr);
+ }
+ }
+
/* Must have valid elfcorehdr index */
if (!image->elf_index_valid) {
pr_err("crash hp: unable to locate elfcorehdr segment");
--
2.27.0
Support for CPU and memory hotplug for crash is controlled by the
CRASH_HOTPLUG configuration option, introduced by this patch.
The CRASH_HOTPLUG_ELFCOREHDR_SZ related configuration option is
also introduced with this patch.
Signed-off-by: Eric DeVolder <[email protected]>
---
arch/x86/Kconfig | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9f5bd41bf660..37eb26563f07 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2061,6 +2061,32 @@ config CRASH_DUMP
(CONFIG_RELOCATABLE=y).
For more details see Documentation/admin-guide/kdump/kdump.rst
+config CRASH_HOTPLUG
+ bool "kernel updates of crash elfcorehdr"
+ depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG) && KEXEC_FILE
+ help
+ Enable the kernel to update the crash elfcorehdr (which contains
+ the list of CPUs and memory regions) directly when hot plug/unplug
+ of CPUs or memory. Otherwise userspace must monitor these hot
+ plug/unplug change notifications via udev in order to
+ unload-then-reload the crash kernel so that the list of CPUs and
+ memory regions is kept up-to-date. Note that the udev CPU and
+ memory change notifications still occur (however, userspace is not
+ required to monitor for crash dump purposes).
+
+config CRASH_HOTPLUG_ELFCOREHDR_SZ
+ depends on CRASH_HOTPLUG
+ int
+ default 131072
+ help
+ Specify the maximum size of the elfcorehdr buffer/segment.
+ The 128KiB default is sized so that it can accommodate 2048
+ Elf64_Phdr, where each Phdr represents either a CPU or a
+ region of memory.
+ For example, this size can accommodate a machine with up to 1024
+ CPUs and up to 1024 memory regions, eg. as represented by the
+ 'System RAM' entries in /proc/iomem.
+
config KEXEC_JUMP
bool "kexec jump"
depends on KEXEC && HIBERNATION
--
2.27.0
On 03/03/22 at 11:27am, Eric DeVolder wrote:
> Support for CPU and memory hotplug for crash is controlled by the
> CRASH_HOTPLUG configuration option, introduced by this patch.
>
> The CRASH_HOTPLUG_ELFCOREHDR_SZ related configuration option is
> also introduced with this patch.
Maybe can rephrase it as:
x86/crash: Introduce new options to support cpu and memory hotplug of crash
CRASH_HOTPLUG is to enable cpu and memory hotplug of crash.
CRASH_HOTPLUG_ELFCOREHDR_SZ is used to Specify the maximum size of
the elfcorehdr buffer/segment.
This is a preparation for later usage.
Otherwise, this looks good to me.
>
> Signed-off-by: Eric DeVolder <[email protected]>
> ---
> arch/x86/Kconfig | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 9f5bd41bf660..37eb26563f07 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2061,6 +2061,32 @@ config CRASH_DUMP
> (CONFIG_RELOCATABLE=y).
> For more details see Documentation/admin-guide/kdump/kdump.rst
>
> +config CRASH_HOTPLUG
> + bool "kernel updates of crash elfcorehdr"
> + depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG) && KEXEC_FILE
> + help
> + Enable the kernel to update the crash elfcorehdr (which contains
> + the list of CPUs and memory regions) directly when hot plug/unplug
> + of CPUs or memory. Otherwise userspace must monitor these hot
> + plug/unplug change notifications via udev in order to
> + unload-then-reload the crash kernel so that the list of CPUs and
> + memory regions is kept up-to-date. Note that the udev CPU and
> + memory change notifications still occur (however, userspace is not
> + required to monitor for crash dump purposes).
> +
> +config CRASH_HOTPLUG_ELFCOREHDR_SZ
> + depends on CRASH_HOTPLUG
> + int
> + default 131072
> + help
> + Specify the maximum size of the elfcorehdr buffer/segment.
> + The 128KiB default is sized so that it can accommodate 2048
> + Elf64_Phdr, where each Phdr represents either a CPU or a
> + region of memory.
> + For example, this size can accommodate a machine with up to 1024
> + CPUs and up to 1024 memory regions, eg. as represented by the
> + 'System RAM' entries in /proc/iomem.
> +
> config KEXEC_JUMP
> bool "kexec jump"
> depends on KEXEC && HIBERNATION
> --
> 2.27.0
>
On 03/03/22 at 11:27am, 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.
>
> 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 if no errors occur, it is
> installed over the top of the existing elfcorehdr.
>
> In the patch 'crash hp: 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_HOTPLUG_ELFCOREHDR_SZ configure item.
>
> With this change, the kexec_file_load syscall (not kexec_load)
> is supported. When loading the crash kernel via kexec_file_load,
> the elfcorehdr is identified at load time in crash_load_segments().
I tune the log a little, please check:
[PATCH v5 7/8] x86/crash: Add x86 crash hotplug support for kexec_file_load
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.
To update the elfcorehdr for x86_64, a new elfcorehdr need be
generated from the available CPUs and memory. The new elfcorehdr
is prepared into a buffer, 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_HOTPLUG_ELFCOREHDR_SZ configure item.
With this change, crash hotplug for kexec_file_load syscall
is supported. When loading kdump kernel via kexec_file_load,
the elfcorehdr is identified at load time in crash_load_segments().
>
>
> Signed-off-by: Eric DeVolder <[email protected]>
> ---
> arch/x86/kernel/crash.c | 120 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 120 insertions(+)
>
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 9db41cce8d97..5da30e2bc780 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>
> @@ -398,7 +399,17 @@ int crash_load_segments(struct kimage *image)
> image->elf_headers = kbuf.buffer;
> image->elf_headers_sz = kbuf.bufsz;
>
> +#ifdef CONFIG_CRASH_HOTPLUG
> + /* Ensure elfcorehdr segment large enough for hotplug changes */
> + kbuf.memsz = CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ;
> + /* For marking as usable to crash kernel */
> + image->elf_headers_sz = kbuf.memsz;
> + /* Record the index of the elfcorehdr segment */
> + image->elf_index = image->nr_segments;
> + image->elf_index_valid = true;
> +#else
> kbuf.memsz = kbuf.bufsz;
> +#endif
> kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
> ret = kexec_add_buffer(&kbuf);
> @@ -413,3 +424,112 @@ int crash_load_segments(struct kimage *image)
> return ret;
> }
> #endif /* CONFIG_KEXEC_FILE */
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> +static void *map_crash_pages(unsigned long paddr, unsigned long size)
> +{
> + /*
> + * 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 *ptr = NULL;
> +
> + /* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */
> + if (size > 0) {
> + struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
> +
> + ptr = kmap(page);
> + }
> +
> + return ptr;
> +}
> +
> +static void unmap_crash_pages(void **ptr)
> +{
> + if (ptr) {
> + if (*ptr)
> + kunmap(*ptr);
> + *ptr = NULL;
> + }
> +}
> +
> +/**
> + * arch_crash_hotplug_handler() - Handle hotplug elfcorehdr changes
> + * @image: the active struct kimage
> + * @hp_action: the hot un/plug action being handled
> + * @a: first parameter dependent upon hp_action
> + * @b: first parameter dependent upon hp_action
> + *
> + * To accurately reflect hot un/plug changes, the elfcorehdr (which
> + * is passed to the crash kernel via the elfcorehdr= parameter)
> + * must be updated with the new list of CPUs and memories. The new
> + * elfcorehdr is prepared in a kernel buffer, and if no errors,
~~~~~~~~~~~~~~~~~~
can be removed.
> + * then it is written on top of the existing/old elfcorehdr.
> + *
> + * For hotplug changes to elfcorehdr to work, two conditions are
> + * needed:
> + * First, the segment containing the elfcorehdr must be large enough
> + * to permit a growing number of resources. See
> + * CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ.
> + * Second, purgatory must explicitly exclude the elfcorehdr from the
> + * list of segments it checks (since the elfcorehdr changes and thus
> + * would require an update to purgatory itself to update the digest).
> + *
> + */
> +void arch_crash_hotplug_handler(struct kimage *image,
> + unsigned int hp_action, unsigned long a, unsigned long b)
> +{
> + struct kexec_segment *ksegment;
> + unsigned char *ptr = NULL;
> + unsigned long elfsz = 0;
> + void *elfbuf = NULL;
> + unsigned long mem, memsz;
> +
> + /* Must have valid elfcorehdr index */
Redundant code comment can be removed.
> + if (!image->elf_index_valid) {
> + pr_err("crash hp: unable to locate elfcorehdr segment");
> + goto out;
> + }
> +
> + ksegment = &image->segment[image->elf_index];
> + mem = ksegment->mem;
> + memsz = ksegment->memsz;
> +
> + /*
> + * Create the new elfcorehdr reflecting the changes to CPU and/or
> + * memory resources. The elfcorehdr segment memsz must be
> + * sufficiently large to accommodate increases due to hotplug
> + * activity. See CRASH_HOTPLUG_ELFCOREHDR_SZ.
> + */
This paragraph could be duplicated with the part in kernel-doc.
Considering to drop one?
> + if (prepare_elf_headers(image, &elfbuf, &elfsz)) {
> + pr_err("crash hp: unable to prepare elfcore headers");
> + goto out;
> + }
> + 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.
> + * Copy new elfcorehdr into destination.
> + */
> + ptr = map_crash_pages(mem, memsz);
> + if (ptr) {
> + /* Temporarily invalidate the crash image while it is replaced */
> + xchg(&kexec_crash_image, NULL);
> + /* Write the new elfcorehdr into memory */
No need, the code is self explanatory.
> + memcpy_flushcache((void *)ptr, elfbuf, elfsz);
> + /* The crash image is now valid once again */
ditto. Sometime over commenting is not suggested.
> + xchg(&kexec_crash_image, image);
> + }
> + unmap_crash_pages((void **)&ptr);
> + pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
> +
> +out:
> + if (elfbuf)
> + vfree(elfbuf);
> +}
> +#endif /* CONFIG_CRASH_HOTPLUG */
> --
> 2.27.0
>
On 03/03/22 at 11:27am, Eric DeVolder wrote:
> For kexec_file_load support, the loading of the crash kernel occurs
> entirely within the kernel, and as such the elfcorehdr is readily
> identified (so that it can be modified upon hotplug events).
>
> This change enables support for kexec_load by identifying the
> elfcorehdr segment in the arch_crash_hotplug_handler(), if it has
> not already been identified.
>
> In general, support for kexec_load requires corresponding changes
> to the userspace kexec-tools utility. It is the responsibility of
> the userspace kexec utility to ensure that:
> - the elfcorehdr segment is sufficiently large enough to accommodate
> hotplug changes, ala CRASH_HOTPLUG_ELFCOREHDR_SZ.
> - provides a purgatory that excludes the elfcorehdr from its list of
> run-time segments to check.
> These changes to the userspace kexec utility are available, but not
> yet accepted upstream.
These backgroud information should be put in cover letter, or in patch
where they won't be grabbed into the final commit log.
>
> Signed-off-by: Eric DeVolder <[email protected]>
> ---
Here, if you want to put some status or backgroud information and expect
they are not got into log, this is a appropriate place.
> arch/x86/kernel/crash.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 5da30e2bc780..45cc6e3af63e 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -486,6 +486,32 @@ void arch_crash_hotplug_handler(struct kimage *image,
> void *elfbuf = NULL;
> unsigned long mem, memsz;
>
> + /*
> + * When the struct kimage is alloced, it is wiped to zero, so
> + * the elf_index_valid defaults to false. It is set on the
> + * kexec_file_load path, or here for kexec_load.
I would make the last line as:
kexec_file_load path, or here for kexec_load if not already
identified..
> + */
> + if (!image->elf_index_valid) {
> + unsigned int n;
> +
> + for (n = 0; n < image->nr_segments; n++) {
> + mem = image->segment[n].mem;
> + memsz = image->segment[n].memsz;
> + ptr = map_crash_pages(mem, memsz);
> + if (ptr) {
> + /* The segment containing elfcorehdr */
> + if ((ptr[0] == 0x7F) &&
> + (ptr[1] == 'E') &&
> + (ptr[2] == 'L') &&
> + (ptr[3] == 'F')) {
Can it be like memcmp(ptr, ELFMAG, SELFMAG) as we have done in
parse_crash_elf_headers()? With that, one line is taken.
> + image->elf_index = (int)n;
> + image->elf_index_valid = true;
> + }
> + }
> + unmap_crash_pages((void **)&ptr);
> + }
> + }
> +
> /* Must have valid elfcorehdr index */
> if (!image->elf_index_valid) {
> pr_err("crash hp: unable to locate elfcorehdr segment");
> --
> 2.27.0
>
On 3/31/22 06:10, Baoquan He wrote:
> On 03/03/22 at 11:27am, Eric DeVolder wrote:
>> For kexec_file_load support, the loading of the crash kernel occurs
>> entirely within the kernel, and as such the elfcorehdr is readily
>> identified (so that it can be modified upon hotplug events).
>>
>> This change enables support for kexec_load by identifying the
>> elfcorehdr segment in the arch_crash_hotplug_handler(), if it has
>> not already been identified.
>>
>> In general, support for kexec_load requires corresponding changes
>> to the userspace kexec-tools utility. It is the responsibility of
>> the userspace kexec utility to ensure that:
>> - the elfcorehdr segment is sufficiently large enough to accommodate
>> hotplug changes, ala CRASH_HOTPLUG_ELFCOREHDR_SZ.
>> - provides a purgatory that excludes the elfcorehdr from its list of
>> run-time segments to check.
>> These changes to the userspace kexec utility are available, but not
>> yet accepted upstream.
>
> These backgroud information should be put in cover letter, or in patch
> where they won't be grabbed into the final commit log.
Removed.
>
>>
>> Signed-off-by: Eric DeVolder <[email protected]>
>> ---
> Here, if you want to put some status or backgroud information and expect
> they are not got into log, this is a appropriate place.
>
>
>> arch/x86/kernel/crash.c | 26 ++++++++++++++++++++++++++
>> 1 file changed, 26 insertions(+)
>>
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 5da30e2bc780..45cc6e3af63e 100644
>> --- a/arch/x86/kernel/crash.c
>> +++ b/arch/x86/kernel/crash.c
>> @@ -486,6 +486,32 @@ void arch_crash_hotplug_handler(struct kimage *image,
>> void *elfbuf = NULL;
>> unsigned long mem, memsz;
>>
>> + /*
>> + * When the struct kimage is alloced, it is wiped to zero, so
>> + * the elf_index_valid defaults to false. It is set on the
>> + * kexec_file_load path, or here for kexec_load.
>
> I would make the last line as:
> kexec_file_load path, or here for kexec_load if not already
> identified..
done
>
>> + */
>> + if (!image->elf_index_valid) {
>> + unsigned int n;
>> +
>> + for (n = 0; n < image->nr_segments; n++) {
>> + mem = image->segment[n].mem;
>> + memsz = image->segment[n].memsz;
>> + ptr = map_crash_pages(mem, memsz);
>> + if (ptr) {
>> + /* The segment containing elfcorehdr */
>> + if ((ptr[0] == 0x7F) &&
>> + (ptr[1] == 'E') &&
>> + (ptr[2] == 'L') &&
>> + (ptr[3] == 'F')) {
>
> Can it be like memcmp(ptr, ELFMAG, SELFMAG) as we have done in
> parse_crash_elf_headers()? With that, one line is taken.
done
>
>> + image->elf_index = (int)n;
>> + image->elf_index_valid = true;
>> + }
>> + }
>> + unmap_crash_pages((void **)&ptr);
>> + }
>> + }
>> +
>> /* Must have valid elfcorehdr index */
>> if (!image->elf_index_valid) {
>> pr_err("crash hp: unable to locate elfcorehdr segment");
>> --
>> 2.27.0
>>
>
On 3/31/22 05:34, Baoquan He wrote:
> On 03/03/22 at 11:27am, 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.
>>
>> 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 if no errors occur, it is
>> installed over the top of the existing elfcorehdr.
>>
>> In the patch 'crash hp: 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_HOTPLUG_ELFCOREHDR_SZ configure item.
>>
>> With this change, the kexec_file_load syscall (not kexec_load)
>> is supported. When loading the crash kernel via kexec_file_load,
>> the elfcorehdr is identified at load time in crash_load_segments().
>
> I tune the log a little, please check:
>
> [PATCH v5 7/8] x86/crash: Add x86 crash hotplug support for kexec_file_load
>
> 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.
>
> To update the elfcorehdr for x86_64, a new elfcorehdr need be
> generated from the available CPUs and memory. The new elfcorehdr
> is prepared into a buffer, 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_HOTPLUG_ELFCOREHDR_SZ configure item.
>
> With this change, crash hotplug for kexec_file_load syscall
> is supported. When loading kdump kernel via kexec_file_load,
> the elfcorehdr is identified at load time in crash_load_segments().
>
Updated the commit message.
>>
>
>>
>> Signed-off-by: Eric DeVolder <[email protected]>
>> ---
>> arch/x86/kernel/crash.c | 120 ++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 120 insertions(+)
>>
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 9db41cce8d97..5da30e2bc780 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>
>> @@ -398,7 +399,17 @@ int crash_load_segments(struct kimage *image)
>> image->elf_headers = kbuf.buffer;
>> image->elf_headers_sz = kbuf.bufsz;
>>
>> +#ifdef CONFIG_CRASH_HOTPLUG
>> + /* Ensure elfcorehdr segment large enough for hotplug changes */
>> + kbuf.memsz = CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ;
>> + /* For marking as usable to crash kernel */
>> + image->elf_headers_sz = kbuf.memsz;
>> + /* Record the index of the elfcorehdr segment */
>> + image->elf_index = image->nr_segments;
>> + image->elf_index_valid = true;
>> +#else
>> kbuf.memsz = kbuf.bufsz;
>> +#endif
>> kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
>> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>> ret = kexec_add_buffer(&kbuf);
>> @@ -413,3 +424,112 @@ int crash_load_segments(struct kimage *image)
>> return ret;
>> }
>> #endif /* CONFIG_KEXEC_FILE */
>> +
>> +#ifdef CONFIG_CRASH_HOTPLUG
>> +static void *map_crash_pages(unsigned long paddr, unsigned long size)
>> +{
>> + /*
>> + * 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 *ptr = NULL;
>> +
>> + /* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */
>> + if (size > 0) {
>> + struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
>> +
>> + ptr = kmap(page);
>> + }
>> +
>> + return ptr;
>> +}
>> +
>> +static void unmap_crash_pages(void **ptr)
>> +{
>> + if (ptr) {
>> + if (*ptr)
>> + kunmap(*ptr);
>> + *ptr = NULL;
>> + }
>> +}
>> +
>> +/**
>> + * arch_crash_hotplug_handler() - Handle hotplug elfcorehdr changes
>> + * @image: the active struct kimage
>> + * @hp_action: the hot un/plug action being handled
>> + * @a: first parameter dependent upon hp_action
>> + * @b: first parameter dependent upon hp_action
>> + *
>> + * To accurately reflect hot un/plug changes, the elfcorehdr (which
>> + * is passed to the crash kernel via the elfcorehdr= parameter)
>> + * must be updated with the new list of CPUs and memories. The new
>> + * elfcorehdr is prepared in a kernel buffer, and if no errors,
> ~~~~~~~~~~~~~~~~~~
> can be removed.
done
>> + * then it is written on top of the existing/old elfcorehdr.
>> + *
>> + * For hotplug changes to elfcorehdr to work, two conditions are
>> + * needed:
>> + * First, the segment containing the elfcorehdr must be large enough
>> + * to permit a growing number of resources. See
>> + * CONFIG_CRASH_HOTPLUG_ELFCOREHDR_SZ.
>> + * Second, purgatory must explicitly exclude the elfcorehdr from the
>> + * list of segments it checks (since the elfcorehdr changes and thus
>> + * would require an update to purgatory itself to update the digest).
>> + *
>> + */
>> +void arch_crash_hotplug_handler(struct kimage *image,
>> + unsigned int hp_action, unsigned long a, unsigned long b)
>> +{
>> + struct kexec_segment *ksegment;
>> + unsigned char *ptr = NULL;
>> + unsigned long elfsz = 0;
>> + void *elfbuf = NULL;
>> + unsigned long mem, memsz;
>> +
>> + /* Must have valid elfcorehdr index */
> Redundant code comment can be removed.
done
>
>> + if (!image->elf_index_valid) {
>> + pr_err("crash hp: unable to locate elfcorehdr segment");
>> + goto out;
>> + }
>> +
>> + ksegment = &image->segment[image->elf_index];
>> + mem = ksegment->mem;
>> + memsz = ksegment->memsz;
>> +
>> + /*
>> + * Create the new elfcorehdr reflecting the changes to CPU and/or
>> + * memory resources. The elfcorehdr segment memsz must be
>> + * sufficiently large to accommodate increases due to hotplug
>> + * activity. See CRASH_HOTPLUG_ELFCOREHDR_SZ.
>> + */
> This paragraph could be duplicated with the part in kernel-doc.
> Considering to drop one?
done
>> + if (prepare_elf_headers(image, &elfbuf, &elfsz)) {
>> + pr_err("crash hp: unable to prepare elfcore headers");
>> + goto out;
>> + }
>> + 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.
>> + * Copy new elfcorehdr into destination.
>> + */
>> + ptr = map_crash_pages(mem, memsz);
>> + if (ptr) {
>> + /* Temporarily invalidate the crash image while it is replaced */
>> + xchg(&kexec_crash_image, NULL);
>> + /* Write the new elfcorehdr into memory */
> No need, the code is self explanatory.
done
>> + memcpy_flushcache((void *)ptr, elfbuf, elfsz);
>> + /* The crash image is now valid once again */
>
> ditto. Sometime over commenting is not suggested.
done
>
>> + xchg(&kexec_crash_image, image);
>> + }
>> + unmap_crash_pages((void **)&ptr);
>> + pr_debug("crash hp: re-loaded elfcorehdr at 0x%lx\n", mem);
>> +
>> +out:
>> + if (elfbuf)
>> + vfree(elfbuf);
>> +}
>> +#endif /* CONFIG_CRASH_HOTPLUG */
>> --
>> 2.27.0
>>
>
On 3/21/22 06:59, Baoquan He wrote:
> On 03/03/22 at 11:27am, Eric DeVolder wrote:
>> Support for CPU and memory hotplug for crash is controlled by the
>> CRASH_HOTPLUG configuration option, introduced by this patch.
>>
>> The CRASH_HOTPLUG_ELFCOREHDR_SZ related configuration option is
>> also introduced with this patch.
>
> Maybe can rephrase it as:
>
> x86/crash: Introduce new options to support cpu and memory hotplug of crash
>
> CRASH_HOTPLUG is to enable cpu and memory hotplug of crash.
>
> CRASH_HOTPLUG_ELFCOREHDR_SZ is used to Specify the maximum size of
> the elfcorehdr buffer/segment.
>
> This is a preparation for later usage.
>
> Otherwise, this looks good to me.
Commit message updated.
eric
>
>
>>
>> Signed-off-by: Eric DeVolder <[email protected]>
>> ---
>> arch/x86/Kconfig | 26 ++++++++++++++++++++++++++
>> 1 file changed, 26 insertions(+)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 9f5bd41bf660..37eb26563f07 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -2061,6 +2061,32 @@ config CRASH_DUMP
>> (CONFIG_RELOCATABLE=y).
>> For more details see Documentation/admin-guide/kdump/kdump.rst
>>
>> +config CRASH_HOTPLUG
>> + bool "kernel updates of crash elfcorehdr"
>> + depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG) && KEXEC_FILE
>> + help
>> + Enable the kernel to update the crash elfcorehdr (which contains
>> + the list of CPUs and memory regions) directly when hot plug/unplug
>> + of CPUs or memory. Otherwise userspace must monitor these hot
>> + plug/unplug change notifications via udev in order to
>> + unload-then-reload the crash kernel so that the list of CPUs and
>> + memory regions is kept up-to-date. Note that the udev CPU and
>> + memory change notifications still occur (however, userspace is not
>> + required to monitor for crash dump purposes).
>> +
>> +config CRASH_HOTPLUG_ELFCOREHDR_SZ
>> + depends on CRASH_HOTPLUG
>> + int
>> + default 131072
>> + help
>> + Specify the maximum size of the elfcorehdr buffer/segment.
>> + The 128KiB default is sized so that it can accommodate 2048
>> + Elf64_Phdr, where each Phdr represents either a CPU or a
>> + region of memory.
>> + For example, this size can accommodate a machine with up to 1024
>> + CPUs and up to 1024 memory regions, eg. as represented by the
>> + 'System RAM' entries in /proc/iomem.
>> +
>> config KEXEC_JUMP
>> bool "kexec jump"
>> depends on KEXEC && HIBERNATION
>> --
>> 2.27.0
>>
>