xref: /openbmc/linux/kernel/crash_core.c (revision 6f991cc3)

// SPDX-License-Identifier: GPL-2.0-only
/*
 * crash.c - kernel crash support code.
 * Copyright (C) 2002-2004 Eric Biederman  <ebiederm@xmission.com>
 */

#include <linux/buildid.h>
#include <linux/crash_core.h>
#include <linux/init.h>
#include <linux/utsname.h>
#include <linux/vmalloc.h>
#include <linux/sizes.h>
#include <linux/kexec.h>

#include <asm/page.h>
#include <asm/sections.h>

#include <crypto/sha1.h>

#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;
u32 *vmcoreinfo_note;

/* trusted vmcoreinfo, e.g. we can make a copy in the crash memory */
static unsigned char *vmcoreinfo_data_safecopy;

/*
 * parsing the "crashkernel" commandline
 *
 * this code is intended to be called from architecture specific code
 */


/*
 * This function parses command lines in the format
 *
 *   crashkernel=ramsize-range:size[,...][@offset]
 *
 * The function returns 0 on success and -EINVAL on failure.
 */
static int __init parse_crashkernel_mem(char *cmdline,
					unsigned long long system_ram,
					unsigned long long *crash_size,
					unsigned long long *crash_base)
{
	char *cur = cmdline, *tmp;
	unsigned long long total_mem = system_ram;

	/*
	 * Firmware sometimes reserves some memory regions for its own use,
	 * so the system memory size is less than the actual physical memory
	 * size. Work around this by rounding up the total size to 128M,
	 * which is enough for most test cases.
	 */
	total_mem = roundup(total_mem, SZ_128M);

	/* for each entry of the comma-separated list */
	do {
		unsigned long long start, end = ULLONG_MAX, size;

		/* get the start of the range */
		start = memparse(cur, &tmp);
		if (cur == tmp) {
			pr_warn("crashkernel: Memory value expected\n");
			return -EINVAL;
		}
		cur = tmp;
		if (*cur != '-') {
			pr_warn("crashkernel: '-' expected\n");
			return -EINVAL;
		}
		cur++;

		/* if no ':' is here, than we read the end */
		if (*cur != ':') {
			end = memparse(cur, &tmp);
			if (cur == tmp) {
				pr_warn("crashkernel: Memory value expected\n");
				return -EINVAL;
			}
			cur = tmp;
			if (end <= start) {
				pr_warn("crashkernel: end <= start\n");
				return -EINVAL;
			}
		}

		if (*cur != ':') {
			pr_warn("crashkernel: ':' expected\n");
			return -EINVAL;
		}
		cur++;

		size = memparse(cur, &tmp);
		if (cur == tmp) {
			pr_warn("Memory value expected\n");
			return -EINVAL;
		}
		cur = tmp;
		if (size >= total_mem) {
			pr_warn("crashkernel: invalid size\n");
			return -EINVAL;
		}

		/* match ? */
		if (total_mem >= start && total_mem < end) {
			*crash_size = size;
			break;
		}
	} while (*cur++ == ',');

	if (*crash_size > 0) {
		while (*cur && *cur != ' ' && *cur != '@')
			cur++;
		if (*cur == '@') {
			cur++;
			*crash_base = memparse(cur, &tmp);
			if (cur == tmp) {
				pr_warn("Memory value expected after '@'\n");
				return -EINVAL;
			}
		}
	} else
		pr_info("crashkernel size resulted in zero bytes\n");

	return 0;
}

/*
 * That function parses "simple" (old) crashkernel command lines like
 *
 *	crashkernel=size[@offset]
 *
 * It returns 0 on success and -EINVAL on failure.
 */
static int __init parse_crashkernel_simple(char *cmdline,
					   unsigned long long *crash_size,
					   unsigned long long *crash_base)
{
	char *cur = cmdline;

	*crash_size = memparse(cmdline, &cur);
	if (cmdline == cur) {
		pr_warn("crashkernel: memory value expected\n");
		return -EINVAL;
	}

	if (*cur == '@')
		*crash_base = memparse(cur+1, &cur);
	else if (*cur != ' ' && *cur != '\0') {
		pr_warn("crashkernel: unrecognized char: %c\n", *cur);
		return -EINVAL;
	}

	return 0;
}

#define SUFFIX_HIGH 0
#define SUFFIX_LOW  1
#define SUFFIX_NULL 2
static __initdata char *suffix_tbl[] = {
	[SUFFIX_HIGH] = ",high",
	[SUFFIX_LOW]  = ",low",
	[SUFFIX_NULL] = NULL,
};

/*
 * That function parses "suffix"  crashkernel command lines like
 *
 *	crashkernel=size,[high|low]
 *
 * It returns 0 on success and -EINVAL on failure.
 */
static int __init parse_crashkernel_suffix(char *cmdline,
					   unsigned long long	*crash_size,
					   const char *suffix)
{
	char *cur = cmdline;

	*crash_size = memparse(cmdline, &cur);
	if (cmdline == cur) {
		pr_warn("crashkernel: memory value expected\n");
		return -EINVAL;
	}

	/* check with suffix */
	if (strncmp(cur, suffix, strlen(suffix))) {
		pr_warn("crashkernel: unrecognized char: %c\n", *cur);
		return -EINVAL;
	}
	cur += strlen(suffix);
	if (*cur != ' ' && *cur != '\0') {
		pr_warn("crashkernel: unrecognized char: %c\n", *cur);
		return -EINVAL;
	}

	return 0;
}

static __init char *get_last_crashkernel(char *cmdline,
			     const char *name,
			     const char *suffix)
{
	char *p = cmdline, *ck_cmdline = NULL;

	/* find crashkernel and use the last one if there are more */
	p = strstr(p, name);
	while (p) {
		char *end_p = strchr(p, ' ');
		char *q;

		if (!end_p)
			end_p = p + strlen(p);

		if (!suffix) {
			int i;

			/* skip the one with any known suffix */
			for (i = 0; suffix_tbl[i]; i++) {
				q = end_p - strlen(suffix_tbl[i]);
				if (!strncmp(q, suffix_tbl[i],
					     strlen(suffix_tbl[i])))
					goto next;
			}
			ck_cmdline = p;
		} else {
			q = end_p - strlen(suffix);
			if (!strncmp(q, suffix, strlen(suffix)))
				ck_cmdline = p;
		}
next:
		p = strstr(p+1, name);
	}

	return ck_cmdline;
}

static int __init __parse_crashkernel(char *cmdline,
			     unsigned long long system_ram,
			     unsigned long long *crash_size,
			     unsigned long long *crash_base,
			     const char *name,
			     const char *suffix)
{
	char	*first_colon, *first_space;
	char	*ck_cmdline;

	BUG_ON(!crash_size || !crash_base);
	*crash_size = 0;
	*crash_base = 0;

	ck_cmdline = get_last_crashkernel(cmdline, name, suffix);
	if (!ck_cmdline)
		return -ENOENT;

	ck_cmdline += strlen(name);

	if (suffix)
		return parse_crashkernel_suffix(ck_cmdline, crash_size,
				suffix);
	/*
	 * if the commandline contains a ':', then that's the extended
	 * syntax -- if not, it must be the classic syntax
	 */
	first_colon = strchr(ck_cmdline, ':');
	first_space = strchr(ck_cmdline, ' ');
	if (first_colon && (!first_space || first_colon < first_space))
		return parse_crashkernel_mem(ck_cmdline, system_ram,
				crash_size, crash_base);

	return parse_crashkernel_simple(ck_cmdline, crash_size, crash_base);
}

/*
 * That function is the entry point for command line parsing and should be
 * called from the arch-specific code.
 */
int __init parse_crashkernel(char *cmdline,
			     unsigned long long system_ram,
			     unsigned long long *crash_size,
			     unsigned long long *crash_base)
{
	return __parse_crashkernel(cmdline, system_ram, crash_size, crash_base,
					"crashkernel=", NULL);
}

int __init parse_crashkernel_high(char *cmdline,
			     unsigned long long system_ram,
			     unsigned long long *crash_size,
			     unsigned long long *crash_base)
{
	return __parse_crashkernel(cmdline, system_ram, crash_size, crash_base,
				"crashkernel=", suffix_tbl[SUFFIX_HIGH]);
}

int __init parse_crashkernel_low(char *cmdline,
			     unsigned long long system_ram,
			     unsigned long long *crash_size,
			     unsigned long long *crash_base)
{
	return __parse_crashkernel(cmdline, system_ram, crash_size, crash_base,
				"crashkernel=", suffix_tbl[SUFFIX_LOW]);
}

/*
 * Add a dummy early_param handler to mark crashkernel= as a known command line
 * parameter and suppress incorrect warnings in init/main.c.
 */
static int __init parse_crashkernel_dummy(char *arg)
{
	return 0;
}
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)
{
	struct elf_note *note = (struct elf_note *)buf;

	note->n_namesz = strlen(name) + 1;
	note->n_descsz = data_len;
	note->n_type   = type;
	buf += DIV_ROUND_UP(sizeof(*note), sizeof(Elf_Word));
	memcpy(buf, name, note->n_namesz);
	buf += DIV_ROUND_UP(note->n_namesz, sizeof(Elf_Word));
	memcpy(buf, data, data_len);
	buf += DIV_ROUND_UP(data_len, sizeof(Elf_Word));

	return buf;
}

void final_note(Elf_Word *buf)
{
	memset(buf, 0, sizeof(struct elf_note));
}

static void update_vmcoreinfo_note(void)
{
	u32 *buf = vmcoreinfo_note;

	if (!vmcoreinfo_size)
		return;
	buf = append_elf_note(buf, VMCOREINFO_NOTE_NAME, 0, vmcoreinfo_data,
			      vmcoreinfo_size);
	final_note(buf);
}

void crash_update_vmcoreinfo_safecopy(void *ptr)
{
	if (ptr)
		memcpy(ptr, vmcoreinfo_data, vmcoreinfo_size);

	vmcoreinfo_data_safecopy = ptr;
}

void crash_save_vmcoreinfo(void)
{
	if (!vmcoreinfo_note)
		return;

	/* Use the safe copy to generate vmcoreinfo note if have */
	if (vmcoreinfo_data_safecopy)
		vmcoreinfo_data = vmcoreinfo_data_safecopy;

	vmcoreinfo_append_str("CRASHTIME=%lld\n", ktime_get_real_seconds());
	update_vmcoreinfo_note();
}

void vmcoreinfo_append_str(const char *fmt, ...)
{
	va_list args;
	char buf[0x50];
	size_t r;

	va_start(args, fmt);
	r = vscnprintf(buf, sizeof(buf), fmt, args);
	va_end(args);

	r = min(r, (size_t)VMCOREINFO_BYTES - vmcoreinfo_size);

	memcpy(&vmcoreinfo_data[vmcoreinfo_size], buf, r);

	vmcoreinfo_size += r;

	WARN_ONCE(vmcoreinfo_size == VMCOREINFO_BYTES,
		  "vmcoreinfo data exceeds allocated size, truncating");
}

/*
 * provide an empty default implementation here -- architecture
 * code may override this
 */
void __weak arch_crash_save_vmcoreinfo(void)
{}

phys_addr_t __weak paddr_vmcoreinfo_note(void)
{
	return __pa(vmcoreinfo_note);
}
EXPORT_SYMBOL(paddr_vmcoreinfo_note);

static int __init crash_save_vmcoreinfo_init(void)
{
	vmcoreinfo_data = (unsigned char *)get_zeroed_page(GFP_KERNEL);
	if (!vmcoreinfo_data) {
		pr_warn("Memory allocation for vmcoreinfo_data failed\n");
		return -ENOMEM;
	}

	vmcoreinfo_note = alloc_pages_exact(VMCOREINFO_NOTE_SIZE,
						GFP_KERNEL | __GFP_ZERO);
	if (!vmcoreinfo_note) {
		free_page((unsigned long)vmcoreinfo_data);
		vmcoreinfo_data = NULL;
		pr_warn("Memory allocation for vmcoreinfo_note failed\n");
		return -ENOMEM;
	}

	VMCOREINFO_OSRELEASE(init_uts_ns.name.release);
	VMCOREINFO_BUILD_ID();
	VMCOREINFO_PAGESIZE(PAGE_SIZE);

	VMCOREINFO_SYMBOL(init_uts_ns);
	VMCOREINFO_OFFSET(uts_namespace, name);
	VMCOREINFO_SYMBOL(node_online_map);
#ifdef CONFIG_MMU
	VMCOREINFO_SYMBOL_ARRAY(swapper_pg_dir);
#endif
	VMCOREINFO_SYMBOL(_stext);
	VMCOREINFO_SYMBOL(vmap_area_list);

#ifndef CONFIG_NUMA
	VMCOREINFO_SYMBOL(mem_map);
	VMCOREINFO_SYMBOL(contig_page_data);
#endif
#ifdef CONFIG_SPARSEMEM
	VMCOREINFO_SYMBOL_ARRAY(mem_section);
	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
	VMCOREINFO_STRUCT_SIZE(mem_section);
	VMCOREINFO_OFFSET(mem_section, section_mem_map);
	VMCOREINFO_NUMBER(SECTION_SIZE_BITS);
	VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
#endif
	VMCOREINFO_STRUCT_SIZE(page);
	VMCOREINFO_STRUCT_SIZE(pglist_data);
	VMCOREINFO_STRUCT_SIZE(zone);
	VMCOREINFO_STRUCT_SIZE(free_area);
	VMCOREINFO_STRUCT_SIZE(list_head);
	VMCOREINFO_SIZE(nodemask_t);
	VMCOREINFO_OFFSET(page, flags);
	VMCOREINFO_OFFSET(page, _refcount);
	VMCOREINFO_OFFSET(page, mapping);
	VMCOREINFO_OFFSET(page, lru);
	VMCOREINFO_OFFSET(page, _mapcount);
	VMCOREINFO_OFFSET(page, private);
	VMCOREINFO_OFFSET(folio, _folio_dtor);
	VMCOREINFO_OFFSET(folio, _folio_order);
	VMCOREINFO_OFFSET(page, compound_head);
	VMCOREINFO_OFFSET(pglist_data, node_zones);
	VMCOREINFO_OFFSET(pglist_data, nr_zones);
#ifdef CONFIG_FLATMEM
	VMCOREINFO_OFFSET(pglist_data, node_mem_map);
#endif
	VMCOREINFO_OFFSET(pglist_data, node_start_pfn);
	VMCOREINFO_OFFSET(pglist_data, node_spanned_pages);
	VMCOREINFO_OFFSET(pglist_data, node_id);
	VMCOREINFO_OFFSET(zone, free_area);
	VMCOREINFO_OFFSET(zone, vm_stat);
	VMCOREINFO_OFFSET(zone, spanned_pages);
	VMCOREINFO_OFFSET(free_area, free_list);
	VMCOREINFO_OFFSET(list_head, next);
	VMCOREINFO_OFFSET(list_head, prev);
	VMCOREINFO_OFFSET(vmap_area, va_start);
	VMCOREINFO_OFFSET(vmap_area, list);
	VMCOREINFO_LENGTH(zone.free_area, MAX_ORDER + 1);
	log_buf_vmcoreinfo_setup();
	VMCOREINFO_LENGTH(free_area.free_list, MIGRATE_TYPES);
	VMCOREINFO_NUMBER(NR_FREE_PAGES);
	VMCOREINFO_NUMBER(PG_lru);
	VMCOREINFO_NUMBER(PG_private);
	VMCOREINFO_NUMBER(PG_swapcache);
	VMCOREINFO_NUMBER(PG_swapbacked);
	VMCOREINFO_NUMBER(PG_slab);
#ifdef CONFIG_MEMORY_FAILURE
	VMCOREINFO_NUMBER(PG_hwpoison);
#endif
	VMCOREINFO_NUMBER(PG_head_mask);
#define PAGE_BUDDY_MAPCOUNT_VALUE	(~PG_buddy)
	VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE);
#ifdef CONFIG_HUGETLB_PAGE
	VMCOREINFO_NUMBER(HUGETLB_PAGE_DTOR);
#define PAGE_OFFLINE_MAPCOUNT_VALUE	(~PG_offline)
	VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE);
#endif

#ifdef CONFIG_KALLSYMS
	VMCOREINFO_SYMBOL(kallsyms_names);
	VMCOREINFO_SYMBOL(kallsyms_num_syms);
	VMCOREINFO_SYMBOL(kallsyms_token_table);
	VMCOREINFO_SYMBOL(kallsyms_token_index);
#ifdef CONFIG_KALLSYMS_BASE_RELATIVE
	VMCOREINFO_SYMBOL(kallsyms_offsets);
	VMCOREINFO_SYMBOL(kallsyms_relative_base);
#else
	VMCOREINFO_SYMBOL(kallsyms_addresses);
#endif /* CONFIG_KALLSYMS_BASE_RELATIVE */
#endif /* CONFIG_KALLSYMS */

	arch_crash_save_vmcoreinfo();
	update_vmcoreinfo_note();

	return 0;
}

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);