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crash: move a few code bits to setup support of crash hotplug

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Patch series "crash: Kernel handling of CPU and memory hot un/plug", v28.

Once the kdump service is loaded, if changes to CPUs or memory occur,
either by hot un/plug or off/onlining, the crash elfcorehdr must also be
updated.

The elfcorehdr describes to kdump the CPUs and memory in the system, and
any inaccuracies can result in a vmcore with missing 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, purgatory and
elfcorehdr) by the userspace kexec utility.  In the original post I
outlined the significant performance problems related to offloading this
activity to userspace.

This patchset introduces a generic crash handler that registers with the
CPU and memory notifiers.  Upon CPU or memory changes, from either hot
un/plug or off/onlining, 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
elfcorehdr update.

Note the description in patch 'crash: change crash_prepare_elf64_headers()
to for_each_possible_cpu()' and 'x86/crash: optimize CPU changes' that
enables further optimizations related to CPU plug/unplug/online/offline
performance of elfcorehdr 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 updates the 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"

   With this changeset applied, the two rules evaluate to false for
   CPU and memory change events and thus skip the userspace
   unload-then-reload of kdump.

 - 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/2023-May/027049.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.


This patch (of 8):

The crash hotplug support leans on the work for the kexec_file_load()
syscall.  To also support the kexec_load() syscall, a few bits of code
need to be move outside of CONFIG_KEXEC_FILE.  As such, these bits are
moved out of kexec_file.c and into a common location crash_core.c.

In addition, struct crash_mem and crash_notes were moved to new locales so
that PROC_KCORE, which sets CRASH_CORE alone, builds correctly.

No functionality change intended.

Link: https://lkml.kernel.org/r/20230814214446.6659-1-eric.devolder@oracle.com
Link: https://lkml.kernel.org/r/20230814214446.6659-2-eric.devolder@oracle.com
Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Acked-by: Hari Bathini <hbathini@linux.ibm.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Akhil Raj <lf32.dev@gmail.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Mimi Zohar <zohar@linux.ibm.com>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Eric DeVolder 2023-08-14 17:44:39 -04:00 committed by Andrew Morton
parent 3d0b713984
commit 6f991cc363
5 changed files with 238 additions and 233 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
include/linux/crash_core.h
View File

@ -28,6 +28,8 @@
VMCOREINFO_BYTES)
typedef u32 note_buf_t[CRASH_CORE_NOTE_BYTES/4];
/* Per cpu memory for storing cpu states in case of system crash. */
extern note_buf_t __percpu *crash_notes;
void crash_update_vmcoreinfo_safecopy(void *ptr);
void crash_save_vmcoreinfo(void);
@ -84,4 +86,22 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
unsigned long long *crash_size, unsigned long long *crash_base);
/* Alignment required for elf header segment */
#define ELF_CORE_HEADER_ALIGN 4096
struct crash_mem {
unsigned int max_nr_ranges;
unsigned int nr_ranges;
struct range ranges[];
};
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 need_kernel_map,
void **addr, unsigned long *sz);
struct kimage;
struct kexec_segment;
#endif /* LINUX_CRASH_CORE_H */

15
include/linux/kexec.h
View File

@ -230,21 +230,6 @@ static inline int arch_kexec_locate_mem_hole(struct kexec_buf *kbuf)
}
#endif
/* Alignment required for elf header segment */
#define ELF_CORE_HEADER_ALIGN 4096
struct crash_mem {
unsigned int max_nr_ranges;
unsigned int nr_ranges;
struct range ranges[];
};
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 need_kernel_map,
void **addr, unsigned long *sz);
#ifndef arch_kexec_apply_relocations_add
/*
* arch_kexec_apply_relocations_add - apply relocations of type RELA

218
kernel/crash_core.c
View File

@ -10,6 +10,7 @@
#include <linux/utsname.h>
#include <linux/vmalloc.h>
#include <linux/sizes.h>
#include <linux/kexec.h>
#include <asm/page.h>
#include <asm/sections.h>
@ -18,6 +19,9 @@
#include "kallsyms_internal.h"
/* Per cpu memory for storing cpu states in case of system crash. */
note_buf_t __percpu *crash_notes;
/* vmcoreinfo stuff */
unsigned char *vmcoreinfo_data;
size_t vmcoreinfo_size;
@ -314,6 +318,187 @@ static int __init parse_crashkernel_dummy(char *arg)
}
early_param("crashkernel", parse_crashkernel_dummy);
int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
void **addr, unsigned long *sz)
{
Elf64_Ehdr *ehdr;
Elf64_Phdr *phdr;
unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
unsigned char *buf;
unsigned int cpu, i;
unsigned long long notes_addr;
unsigned long mstart, mend;
/* extra phdr for vmcoreinfo ELF note */
nr_phdr = nr_cpus + 1;
nr_phdr += mem->nr_ranges;
/*
* kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
* area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
* I think this is required by tools like gdb. So same physical
* memory will be mapped in two ELF headers. One will contain kernel
* text virtual addresses and other will have __va(physical) addresses.
*/
nr_phdr++;
elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
buf = vzalloc(elf_sz);
if (!buf)
return -ENOMEM;
ehdr = (Elf64_Ehdr *)buf;
phdr = (Elf64_Phdr *)(ehdr + 1);
memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
ehdr->e_ident[EI_CLASS] = ELFCLASS64;
ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
ehdr->e_ident[EI_VERSION] = EV_CURRENT;
ehdr->e_ident[EI_OSABI] = ELF_OSABI;
memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
ehdr->e_type = ET_CORE;
ehdr->e_machine = ELF_ARCH;
ehdr->e_version = EV_CURRENT;
ehdr->e_phoff = sizeof(Elf64_Ehdr);
ehdr->e_ehsize = sizeof(Elf64_Ehdr);
ehdr->e_phentsize = sizeof(Elf64_Phdr);
/* Prepare one phdr of type PT_NOTE for each present CPU */
for_each_present_cpu(cpu) {
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;
phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
(ehdr->e_phnum)++;
phdr++;
}
/* Prepare one PT_NOTE header for vmcoreinfo */
phdr->p_type = PT_NOTE;
phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
(ehdr->e_phnum)++;
phdr++;
/* Prepare PT_LOAD type program header for kernel text region */
if (need_kernel_map) {
phdr->p_type = PT_LOAD;
phdr->p_flags = PF_R|PF_W|PF_X;
phdr->p_vaddr = (unsigned long) _text;
phdr->p_filesz = phdr->p_memsz = _end - _text;
phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
ehdr->e_phnum++;
phdr++;
}
/* Go through all the ranges in mem->ranges[] and prepare phdr */
for (i = 0; i < mem->nr_ranges; i++) {
mstart = mem->ranges[i].start;
mend = mem->ranges[i].end;
phdr->p_type = PT_LOAD;
phdr->p_flags = PF_R|PF_W|PF_X;
phdr->p_offset = mstart;
phdr->p_paddr = mstart;
phdr->p_vaddr = (unsigned long) __va(mstart);
phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
phdr->p_align = 0;
ehdr->e_phnum++;
pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
ehdr->e_phnum, phdr->p_offset);
phdr++;
}
*addr = buf;
*sz = elf_sz;
return 0;
}
int crash_exclude_mem_range(struct crash_mem *mem,
unsigned long long mstart, unsigned long long mend)
{
int i, j;
unsigned long long start, end, p_start, p_end;
struct range temp_range = {0, 0};
for (i = 0; i < mem->nr_ranges; i++) {
start = mem->ranges[i].start;
end = mem->ranges[i].end;
p_start = mstart;
p_end = mend;
if (mstart > end || mend < start)
continue;
/* Truncate any area outside of range */
if (mstart < start)
p_start = start;
if (mend > end)
p_end = end;
/* Found completely overlapping range */
if (p_start == start && p_end == end) {
mem->ranges[i].start = 0;
mem->ranges[i].end = 0;
if (i < mem->nr_ranges - 1) {
/* Shift rest of the ranges to left */
for (j = i; j < mem->nr_ranges - 1; j++) {
mem->ranges[j].start =
mem->ranges[j+1].start;
mem->ranges[j].end =
mem->ranges[j+1].end;
}
/*
* Continue to check if there are another overlapping ranges
* from the current position because of shifting the above
* mem ranges.
*/
i--;
mem->nr_ranges--;
continue;
}
mem->nr_ranges--;
return 0;
}
if (p_start > start && p_end < end) {
/* Split original range */
mem->ranges[i].end = p_start - 1;
temp_range.start = p_end + 1;
temp_range.end = end;
} else if (p_start != start)
mem->ranges[i].end = p_start - 1;
else
mem->ranges[i].start = p_end + 1;
break;
}
/* If a split happened, add the split to array */
if (!temp_range.end)
return 0;
/* Split happened */
if (i == mem->max_nr_ranges - 1)
return -ENOMEM;
/* Location where new range should go */
j = i + 1;
if (j < mem->nr_ranges) {
/* Move over all ranges one slot towards the end */
for (i = mem->nr_ranges - 1; i >= j; i--)
mem->ranges[i + 1] = mem->ranges[i];
}
mem->ranges[j].start = temp_range.start;
mem->ranges[j].end = temp_range.end;
mem->nr_ranges++;
return 0;
}
Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
void *data, size_t data_len)
{
@ -515,3 +700,36 @@ static int __init crash_save_vmcoreinfo_init(void)
}
subsys_initcall(crash_save_vmcoreinfo_init);
static int __init crash_notes_memory_init(void)
{
/* Allocate memory for saving cpu registers. */
size_t size, align;
/*
* crash_notes could be allocated across 2 vmalloc pages when percpu
* is vmalloc based . vmalloc doesn't guarantee 2 continuous vmalloc
* pages are also on 2 continuous physical pages. In this case the
* 2nd part of crash_notes in 2nd page could be lost since only the
* starting address and size of crash_notes are exported through sysfs.
* Here round up the size of crash_notes to the nearest power of two
* and pass it to __alloc_percpu as align value. This can make sure
* crash_notes is allocated inside one physical page.
*/
size = sizeof(note_buf_t);
align = min(roundup_pow_of_two(sizeof(note_buf_t)), PAGE_SIZE);
/*
* Break compile if size is bigger than PAGE_SIZE since crash_notes
* definitely will be in 2 pages with that.
*/
BUILD_BUG_ON(size > PAGE_SIZE);
crash_notes = __alloc_percpu(size, align);
if (!crash_notes) {
pr_warn("Memory allocation for saving cpu register states failed\n");
return -ENOMEM;
}
return 0;
}
subsys_initcall(crash_notes_memory_init);

37
kernel/kexec_core.c
View File

@ -49,9 +49,6 @@
atomic_t __kexec_lock = ATOMIC_INIT(0);
/* Per cpu memory for storing cpu states in case of system crash. */
note_buf_t __percpu *crash_notes;
/* Flag to indicate we are going to kexec a new kernel */
bool kexec_in_progress = false;
@ -1218,40 +1215,6 @@ void crash_save_cpu(struct pt_regs *regs, int cpu)
final_note(buf);
}
static int __init crash_notes_memory_init(void)
{
/* Allocate memory for saving cpu registers. */
size_t size, align;
/*
* crash_notes could be allocated across 2 vmalloc pages when percpu
* is vmalloc based . vmalloc doesn't guarantee 2 continuous vmalloc
* pages are also on 2 continuous physical pages. In this case the
* 2nd part of crash_notes in 2nd page could be lost since only the
* starting address and size of crash_notes are exported through sysfs.
* Here round up the size of crash_notes to the nearest power of two
* and pass it to __alloc_percpu as align value. This can make sure
* crash_notes is allocated inside one physical page.
*/
size = sizeof(note_buf_t);
align = min(roundup_pow_of_two(sizeof(note_buf_t)), PAGE_SIZE);
/*
* Break compile if size is bigger than PAGE_SIZE since crash_notes
* definitely will be in 2 pages with that.
*/
BUILD_BUG_ON(size > PAGE_SIZE);
crash_notes = __alloc_percpu(size, align);
if (!crash_notes) {
pr_warn("Memory allocation for saving cpu register states failed\n");
return -ENOMEM;
}
return 0;
}
subsys_initcall(crash_notes_memory_init);
/*
* Move into place and start executing a preloaded standalone
* executable. If nothing was preloaded return an error.

181
kernel/kexec_file.c
View File

@ -1151,184 +1151,3 @@ int kexec_purgatory_get_set_symbol(struct kimage *image, const char *name,
return 0;
}
#endif /* CONFIG_ARCH_SUPPORTS_KEXEC_PURGATORY */
int crash_exclude_mem_range(struct crash_mem *mem,
unsigned long long mstart, unsigned long long mend)
{
int i, j;
unsigned long long start, end, p_start, p_end;
struct range temp_range = {0, 0};
for (i = 0; i < mem->nr_ranges; i++) {
start = mem->ranges[i].start;
end = mem->ranges[i].end;
p_start = mstart;
p_end = mend;
if (mstart > end || mend < start)
continue;
/* Truncate any area outside of range */
if (mstart < start)
p_start = start;
if (mend > end)
p_end = end;
/* Found completely overlapping range */
if (p_start == start && p_end == end) {
mem->ranges[i].start = 0;
mem->ranges[i].end = 0;
if (i < mem->nr_ranges - 1) {
/* Shift rest of the ranges to left */
for (j = i; j < mem->nr_ranges - 1; j++) {
mem->ranges[j].start =
mem->ranges[j+1].start;
mem->ranges[j].end =
mem->ranges[j+1].end;
}
/*
* Continue to check if there are another overlapping ranges
* from the current position because of shifting the above
* mem ranges.
*/
i--;
mem->nr_ranges--;
continue;
}
mem->nr_ranges--;
return 0;
}
if (p_start > start && p_end < end) {
/* Split original range */
mem->ranges[i].end = p_start - 1;
temp_range.start = p_end + 1;
temp_range.end = end;
} else if (p_start != start)
mem->ranges[i].end = p_start - 1;
else
mem->ranges[i].start = p_end + 1;
break;
}
/* If a split happened, add the split to array */
if (!temp_range.end)
return 0;
/* Split happened */
if (i == mem->max_nr_ranges - 1)
return -ENOMEM;
/* Location where new range should go */
j = i + 1;
if (j < mem->nr_ranges) {
/* Move over all ranges one slot towards the end */
for (i = mem->nr_ranges - 1; i >= j; i--)
mem->ranges[i + 1] = mem->ranges[i];
}
mem->ranges[j].start = temp_range.start;
mem->ranges[j].end = temp_range.end;
mem->nr_ranges++;
return 0;
}
int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
void **addr, unsigned long *sz)
{
Elf64_Ehdr *ehdr;
Elf64_Phdr *phdr;
unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
unsigned char *buf;
unsigned int cpu, i;
unsigned long long notes_addr;
unsigned long mstart, mend;
/* extra phdr for vmcoreinfo ELF note */
nr_phdr = nr_cpus + 1;
nr_phdr += mem->nr_ranges;
/*
* kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
* area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
* I think this is required by tools like gdb. So same physical
* memory will be mapped in two ELF headers. One will contain kernel
* text virtual addresses and other will have __va(physical) addresses.
*/
nr_phdr++;
elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
buf = vzalloc(elf_sz);
if (!buf)
return -ENOMEM;
ehdr = (Elf64_Ehdr *)buf;
phdr = (Elf64_Phdr *)(ehdr + 1);
memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
ehdr->e_ident[EI_CLASS] = ELFCLASS64;
ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
ehdr->e_ident[EI_VERSION] = EV_CURRENT;
ehdr->e_ident[EI_OSABI] = ELF_OSABI;
memset(ehdr->e_ident + EI_PAD, 0, EI_NIDENT - EI_PAD);
ehdr->e_type = ET_CORE;
ehdr->e_machine = ELF_ARCH;
ehdr->e_version = EV_CURRENT;
ehdr->e_phoff = sizeof(Elf64_Ehdr);
ehdr->e_ehsize = sizeof(Elf64_Ehdr);
ehdr->e_phentsize = sizeof(Elf64_Phdr);
/* Prepare one phdr of type PT_NOTE for each present CPU */
for_each_present_cpu(cpu) {
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;
phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
(ehdr->e_phnum)++;
phdr++;
}
/* Prepare one PT_NOTE header for vmcoreinfo */
phdr->p_type = PT_NOTE;
phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
(ehdr->e_phnum)++;
phdr++;
/* Prepare PT_LOAD type program header for kernel text region */
if (need_kernel_map) {
phdr->p_type = PT_LOAD;
phdr->p_flags = PF_R|PF_W|PF_X;
phdr->p_vaddr = (unsigned long) _text;
phdr->p_filesz = phdr->p_memsz = _end - _text;
phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
ehdr->e_phnum++;
phdr++;
}
/* Go through all the ranges in mem->ranges[] and prepare phdr */
for (i = 0; i < mem->nr_ranges; i++) {
mstart = mem->ranges[i].start;
mend = mem->ranges[i].end;
phdr->p_type = PT_LOAD;
phdr->p_flags = PF_R|PF_W|PF_X;
phdr->p_offset = mstart;
phdr->p_paddr = mstart;
phdr->p_vaddr = (unsigned long) __va(mstart);
phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
phdr->p_align = 0;
ehdr->e_phnum++;
pr_debug("Crash PT_LOAD ELF header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
ehdr->e_phnum, phdr->p_offset);
phdr++;
}
*addr = buf;
*sz = elf_sz;
return 0;
}