Re: [PATCH v5 2/4] crash: Exclude crash kernel memory in crash core

[Mike Rapoport <rppt@kernel.org>]

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@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 :/
 
> 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.

> +#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 

	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.

> +	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.

> +#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.

>  
> +	/* 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.

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);
}

powerpc could reuse crash_exclude_core_ranges() provided the latter call
an overridable arch_crash_exclude_range()

What do you think?

-- 
Sincerely yours,
Mike.