[PATCH v5 2/4] crash: Exclude crash kernel memory in crash core
Jinjie Ruan
ruanjinjie at huawei.com
Thu Feb 12 19:02:39 PST 2026
On 2026/2/13 2:58, Mike Rapoport wrote:
> Hi,
>
> On Thu, Feb 12, 2026 at 06:09:59PM +0800, Jinjie Ruan wrote:
>> The exclude of crashk_res, crashk_low_res and crashk_cma memory
>> are almost identical across different architectures, handling them
>> in the crash core would eliminate a lot of duplication, so do
>> them in the common code.
>>
>> And move the size calculation (and the realloc if needed) into the
>> generic crash core so that:
>>
>> - New CMA regions or future crash-memory types can automatically
>> accounted for in crash core;
>>
>> - Each architecture no longer has to play whack-a-mole with
>> its private array size.
>>
>> To achieve the above goal, 4 architecture-specific functions are
>> introduced:
>>
>> - arch_get_system_nr_ranges() and arch_prepare_elf64_ram_headers().
>> The 1st function pre-counts the number of memory ranges, and
>> the 2st function fill the memory ranges into the cmem->ranges[] array,
>> and count the actual number of ranges filled.
>
> The names should reflect that these function deal with crash memory ranges.
>
>> - arch_crash_exclude_mem_range(). Realloc for powerpc. The default
>> implementation is crash_exclude_mem_range(), and use
>> crash_exclude_mem_range_guarded() to implement the arch version
>> for powerpc.
>>
>> - arch_get_crash_memory_ranges(). Get crash memory ranges for arch and
>> the default implementation is generic across x86, arm64, riscv, and
>> loongson by using the first two arch functions above. powerpc has its
>> own implementation by calling get_crash_memory_ranges().
>
> Hmm, powerpc seems too different from the rest, maybe we shouldn't try to
> squeeze it in?
>
>> Tested on x86, arm64 and riscv with QEMU.
>>
>> Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
>> ---
>> arch/arm64/include/asm/kexec.h | 9 +-
>> arch/arm64/kernel/machine_kexec_file.c | 41 +++-----
>> arch/loongarch/include/asm/kexec.h | 9 +-
>> arch/loongarch/kernel/machine_kexec_file.c | 41 +++-----
>> arch/powerpc/include/asm/kexec.h | 13 +++
>> arch/powerpc/include/asm/kexec_ranges.h | 3 -
>> arch/powerpc/kexec/crash.c | 68 ++++++++------
>> arch/powerpc/kexec/file_load_64.c | 17 ++--
>> arch/powerpc/kexec/ranges.c | 18 +---
>> arch/riscv/include/asm/kexec.h | 9 +-
>> arch/riscv/kernel/machine_kexec_file.c | 37 +++-----
>> arch/x86/include/asm/kexec.h | 9 ++
>> arch/x86/kernel/crash.c | 104 +++------------------
>> include/linux/crash_core.h | 75 +++++++++++++--
>> kernel/crash_core.c | 85 +++++++++++++++--
>> 15 files changed, 289 insertions(+), 249 deletions(-)
>
> TBH, I'd expect this to produce negative diffstat :/
Forcing compatibility with powerpc has brought a lot of inconvenience.
>
>> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
>> index 892e5bebda95..67f790e3ba14 100644
>> --- a/arch/arm64/include/asm/kexec.h
>> +++ b/arch/arm64/include/asm/kexec.h
>> @@ -119,6 +119,7 @@ struct kimage_arch {
>> };
>>
>> #ifdef CONFIG_KEXEC_FILE
>> +struct crash_mem;
>> extern const struct kexec_file_ops kexec_image_ops;
>>
>> int arch_kimage_file_post_load_cleanup(struct kimage *image);
>> @@ -128,7 +129,13 @@ extern int load_other_segments(struct kimage *image,
>> unsigned long kernel_load_addr, unsigned long kernel_size,
>> char *initrd, unsigned long initrd_len,
>> char *cmdline);
>> -#endif
>> +
>> +int arch_get_system_nr_ranges(unsigned int *nr_ranges);
>> +#define arch_get_system_nr_ranges arch_get_system_nr_ranges
>> +
>> +int arch_prepare_elf64_ram_headers(struct crash_mem *cmem);
>> +#define arch_prepare_elf64_ram_headers arch_prepare_elf64_ram_headers
>
> I think a better practice would be to declare all functions that an
> architecture may override in include/linux/crash_core.h and provide a
> default __weak implementation in kernel/crash_core.c.
This would avoid many function declarations in architecture-specific code.
>
>> +#endif /* CONFIG_KEXEC_FILE */
>>
>> #endif /* __ASSEMBLER__ */
>>
>> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
>> index 410060ebd86d..506a165117b1 100644
>> --- a/arch/arm64/kernel/machine_kexec_file.c
>> +++ b/arch/arm64/kernel/machine_kexec_file.c
>> @@ -40,23 +40,22 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
>> }
>>
>> #ifdef CONFIG_CRASH_DUMP
>> -static int prepare_elf_headers(void **addr, unsigned long *sz)
>> +int arch_get_system_nr_ranges(unsigned int *nr_ranges)
>> {
>> - struct crash_mem *cmem;
>> - unsigned int nr_ranges;
>> - int ret;
>> - u64 i;
>> phys_addr_t start, end;
>> + u64 i;
>>
>> - nr_ranges = 2; /* for exclusion of crashkernel region */
>> for_each_mem_range(i, &start, &end)
>> - nr_ranges++;
>> + (*nr_ranges)++;
>> +
>
> Won't be simpler to make it
This is indeed much cleaner.
>
> unsigned int arch_get_system_nr_ranges(void)
>
> count the ranges and return the result?
>
>> + return 0;
>> +}
>>
>> - cmem = kmalloc(struct_size(cmem, ranges, nr_ranges), GFP_KERNEL);
>> - if (!cmem)
>> - return -ENOMEM;
>> +int arch_prepare_elf64_ram_headers(struct crash_mem *cmem)
>> +{
>
> It seems that this function collects the memory ranges and fills them into
> cmem rather than prepares elf headers.
Yes, the function names were taken from the x86 and riscv
implementations, which caused some confusion.
>
>> + phys_addr_t start, end;
>> + u64 i;
>>
>> - cmem->max_nr_ranges = nr_ranges;
>> cmem->nr_ranges = 0;
>> for_each_mem_range(i, &start, &end) {
>> cmem->ranges[cmem->nr_ranges].start = start;
>> @@ -64,22 +63,7 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
>> cmem->nr_ranges++;
>> }
>>
>> - /* Exclude crashkernel region */
>> - ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
>> - if (ret)
>> - goto out;
>> -
>> - if (crashk_low_res.end) {
>> - ret = crash_exclude_mem_range(cmem, crashk_low_res.start, crashk_low_res.end);
>> - if (ret)
>> - goto out;
>> - }
>> -
>> - ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
>> -
>> -out:
>> - kfree(cmem);
>> - return ret;
>> + return 0;
>> }
>> #endif
>>
>> @@ -109,7 +93,8 @@ int load_other_segments(struct kimage *image,
>> void *headers;
>> unsigned long headers_sz;
>> if (image->type == KEXEC_TYPE_CRASH) {
>> - ret = prepare_elf_headers(&headers, &headers_sz);
>> + ret = crash_prepare_elf64_headers(true, &headers, &headers_sz,
>> + NULL, NULL, NULL);
>> if (ret) {
>> pr_err("Preparing elf core header failed\n");
>> goto out_err;
>
> Same comments as for arm64 apply for other architectures as well.
>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index d35726d6a415..3105d28fd0c6 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -2,11 +2,14 @@
>> #ifndef LINUX_CRASH_CORE_H
>> #define LINUX_CRASH_CORE_H
>>
>> -#include <linux/linkage.h>
>> #include <linux/elfcore.h>
>> #include <linux/elf.h>
>> +#include <linux/kexec.h>
>> +#include <linux/linkage.h>
>> +#include <linux/vmalloc.h>
>>
>> struct kimage;
>> +struct memory_notify;
>>
>> struct crash_mem {
>> unsigned int max_nr_ranges;
>> @@ -54,6 +57,66 @@ static inline int arch_crash_hotplug_support(struct kimage *image, unsigned long
>> }
>> #endif
>>
>> +extern int crash_exclude_mem_range(struct crash_mem *mem,
>> + unsigned long long mstart,
>> + unsigned long long mend);
>> +
>> +#ifndef arch_crash_exclude_mem_range
>> +static __always_inline int arch_crash_exclude_mem_range(struct crash_mem **mem_ranges,
>> + unsigned long long mstart,
>> + unsigned long long mend)
>> +{
>> + return crash_exclude_mem_range(*mem_ranges, mstart, mend);
>> +}
>> +#endif
>> +
>> +#ifndef arch_get_system_nr_ranges
>> +static inline int arch_get_system_nr_ranges(unsigned int *nr_ranges)
>> +{
>> + return -EINVAL;
>> +}
>> +#endif
>> +
>> +#ifndef arch_prepare_elf64_ram_headers
>> +static inline int arch_prepare_elf64_ram_headers(struct crash_mem *cmem)
>> +{
>> + return -EINVAL;
>> +}
>> +#endif
>> +
>> +#ifndef arch_get_crash_memory_ranges
>> +static inline int arch_get_crash_memory_ranges(struct crash_mem **cmem,
>> + unsigned long *nr_mem_ranges,
>> + struct kimage *image,
>> + struct memory_notify *mn)
>> +{
>> + unsigned int nr_ranges;
>> + int ret;
>> +
>> + /*
>> + * Exclusion of crash region, crashk_low_res and/or crashk_cma_ranges
>> + * may cause range splits. So add extra slots here.
>> + */
>> + nr_ranges = 1 + (crashk_low_res.end != 0) + crashk_cma_cnt;
>> + ret = arch_get_system_nr_ranges(&nr_ranges);
>> + if (ret)
>> + return ret;
>> +
>> + *cmem = kvzalloc(struct_size(*cmem, ranges, nr_ranges), GFP_KERNEL);
>> + if (!(*cmem))
>> + return -ENOMEM;
>> +
>> + (*cmem)->max_nr_ranges = nr_ranges;
>> + ret = arch_prepare_elf64_ram_headers(*cmem);
>> + if (ret) {
>> + kvfree(*cmem);
>> + return ret;
>> + }
>> +
>> + return 0;
>> +}
>
> This function is quite large for an inline, should be in
> kernel/crash_core.c IMHO.
Right，inlinie large functions will lead to code bloat.
>
>> +#endif
>> +
>> #ifndef crash_get_elfcorehdr_size
>> static inline unsigned int crash_get_elfcorehdr_size(void) { return 0; }
>> #endif
>> @@ -61,11 +124,11 @@ static inline unsigned int crash_get_elfcorehdr_size(void) { return 0; }
>> /* Alignment required for elf header segment */
>> #define ELF_CORE_HEADER_ALIGN 4096
>>
>> -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);
>> +extern int crash_prepare_elf64_headers(int need_kernel_map,
>> + void **addr, unsigned long *sz,
>> + unsigned long *nr_mem_ranges,
>> + struct kimage *image,
>> + struct memory_notify *mn);
>>
>> struct kimage;
>> struct kexec_segment;
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 99dac1aa972a..99a0d6abf88e 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -18,6 +18,7 @@
>> #include <linux/memblock.h>
>> #include <linux/kmemleak.h>
>> #include <linux/crash_core.h>
>> +#include <linux/crash_reserve.h>
>> #include <linux/reboot.h>
>> #include <linux/btf.h>
>> #include <linux/objtool.h>
>> @@ -161,19 +162,80 @@ static inline resource_size_t crash_resource_size(const struct resource *res)
>> return !res->end ? 0 : resource_size(res);
>> }
>>
>> +static int crash_exclude_mem_ranges(struct crash_mem *cmem,
>> + unsigned long *nr_mem_ranges)
>> +{
>> + int ret, i;
>> +
>> +#if defined(CONFIG_X86_64) || defined(CONFIG_X86_32)
>> + /*
>> + * Exclusion of low 1M may not cause another range split, because the
>> + * range of exclude is [0, 1M] and the condition for splitting a new
>> + * region is that the start, end parameters are both in a certain
>> + * existing region in cmem and cannot be equal to existing region's
>> + * start or end. Obviously, the start of [0, 1M] cannot meet this
>> + * condition.
>> + *
>> + * But in order to lest the low 1M could be changed in the future,
>> + * (e.g. [start, 1M]), add a extra slot.
>> + */
>> + cmem->max_nr_ranges++;
>>
>> + /* Exclude the low 1M because it is always reserved */
>> + ret = arch_crash_exclude_mem_range(&cmem, 0, SZ_1M - 1);
>> + if (ret)
>> + return ret;
>> +#endif
>
> This should remain in x86.
Yes, this should not be in the generic code.
>
>>
>> + /* Exclude crashkernel region */
>> + ret = arch_crash_exclude_mem_range(&cmem, crashk_res.start, crashk_res.end);
>> + if (ret)
>> + return ret;
>>
>> -int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
>> - void **addr, unsigned long *sz)
>> + if (crashk_low_res.end) {
>> + ret = arch_crash_exclude_mem_range(&cmem, crashk_low_res.start, crashk_low_res.end);
>> + if (ret)
>> + return ret;
>> + }
>> +
>> + for (i = 0; i < crashk_cma_cnt; ++i) {
>> + ret = arch_crash_exclude_mem_range(&cmem, crashk_cma_ranges[i].start,
>> + crashk_cma_ranges[i].end);
>> + if (ret)
>> + return ret;
>> + }
>> +
>> + /* Return the computed number of memory ranges, for hotplug usage */
>> + if (nr_mem_ranges)
>> + *nr_mem_ranges = cmem->nr_ranges;
>> +
>> + return 0;
>> +}
>> +
>> +int crash_prepare_elf64_headers(int need_kernel_map, void **addr,
>> + unsigned long *sz, unsigned long *nr_mem_ranges,
>> + struct kimage *image, struct memory_notify *mn)
>
> Hmm, we are adding image and mn parameters only for powerpc and we already
> have arch_crash_exclude_mem_range() and arch_get_crash_memory_ranges() to
> accommodate powerpc differences.
Yes, accommodating powerpc has brought a lot of trouble.
>
> I'd suggest to take a slightly different approach. I'm thinking that we can
> add crash_prepare_elf_headers() that will be similar to current
> x86/arm64/loongarch prepare_elf_headers(), leave
> crash_prepare_elf64_headers() alone and add a helper to exclude common
> ranges, e.g crash_exclude_core_ranges(struct crash_mem *mem).
>
> The crash_prepare_headers() would be something like this (error handling
> omitted):
>
> int crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz)
> {
> unsigned int nr;
> struct crash_mem *cmem;
>
> nr = arch_get_system_nr_ranges();
> cmem = alloc_cmem(nr);
> arch_crash_populate_cmem(cmem);
> crash_exclude_core_ranges(cmem);
> arch_crash_exclude_ranges(cmem);
> crash_prepare_elf64_headers(cmem, need_kernel_map, addr, sz);
> }
This looks fine to me and it can indeed avoid impacting other
architectures that use `crash_prepare_elf64_headers()` but do not use
our generic code.
>
> powerpc could reuse crash_exclude_core_ranges() provided the latter call
> an overridable arch_crash_exclude_range()
We can do this in two steps: first switch x86/arm64/riscv/loongarch to
the above approach, and then switch powerpc over. This will make the
code easier to review.
>
> What do you think?
I think your proposed approach is more elegant and reduces the
disruption to existing code.
>
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