Re: [PATCH v2 6/8] x86: kdump: use generic interface to simplify crashkernel reservation code

[Leizhen (ThunderTown)]

On 2023/8/29 20:16, Baoquan He wrote:
> With the help of newly changed function parse_crashkernel() and
> generic reserve_crashkernel_generic(), crashkernel reservation can be
> simplified by steps:
> 
> 1) Add a new header file <asm/crash_core.h>, and define CRASH_ALIGN,
>    CRASH_ADDR_LOW_MAX, CRASH_ADDR_HIGH_MAX and
>    DEFAULT_CRASH_KERNEL_LOW_SIZE in <asm/crash_core.h>;
> 
> 2) Add arch_reserve_crashkernel() to call parse_crashkernel() and
>    reserve_crashkernel_generic(), and do the ARCH specific work if
>    needed.
> 
> 3) Add ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION Kconfig in
>    arch/x86/Kconfig.
> 
> When adding DEFAULT_CRASH_KERNEL_LOW_SIZE, add crash_low_size_default()
> to calculate crashkernel low memory because x86_64 has special
> requirement.
> 
> The old reserve_crashkernel_low() and reserve_crashkernel() can be
> removed.
> 
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> ---
>  arch/x86/Kconfig                  |   3 +
>  arch/x86/include/asm/crash_core.h |  34 +++++++
>  arch/x86/kernel/setup.c           | 144 ++++--------------------------
>  3 files changed, 53 insertions(+), 128 deletions(-)
>  create mode 100644 arch/x86/include/asm/crash_core.h
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 8d9e4b362572..c4539dc35985 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2037,6 +2037,9 @@ config KEXEC_FILE
>  config ARCH_HAS_KEXEC_PURGATORY
>  	def_bool KEXEC_FILE
>  
> +config ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
> +	def_bool CRASH_CORE
> +
>  config KEXEC_SIG
>  	bool "Verify kernel signature during kexec_file_load() syscall"
>  	depends on KEXEC_FILE
> diff --git a/arch/x86/include/asm/crash_core.h b/arch/x86/include/asm/crash_core.h
> new file mode 100644
> index 000000000000..5fc5e4f94521
> --- /dev/null
> +++ b/arch/x86/include/asm/crash_core.h
> @@ -0,0 +1,34 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _X86_CRASH_CORE_H
> +#define _X86_CRASH_CORE_H
> +
> +/* 16M alignment for crash kernel regions */
> +#define CRASH_ALIGN             SZ_16M
> +
> +/*
> + * Keep the crash kernel below this limit.
> + *
> + * Earlier 32-bits kernels would limit the kernel to the low 512 MB range
> + * due to mapping restrictions.
> + *
> + * 64-bit kdump kernels need to be restricted to be under 64 TB, which is
> + * the upper limit of system RAM in 4-level paging mode. Since the kdump
> + * jump could be from 5-level paging to 4-level paging, the jump will fail if
> + * the kernel is put above 64 TB, and during the 1st kernel bootup there's
> + * no good way to detect the paging mode of the target kernel which will be
> + * loaded for dumping.
> + */
> +
> +#ifdef CONFIG_X86_32
> +# define CRASH_ADDR_LOW_MAX     SZ_512M
> +# define CRASH_ADDR_HIGH_MAX    SZ_512M
> +#else
> +# define CRASH_ADDR_LOW_MAX     SZ_4G
> +# define CRASH_ADDR_HIGH_MAX    SZ_64T
> +#endif
> +
> +# define DEFAULT_CRASH_KERNEL_LOW_SIZE crash_low_size_default()
> +
> +extern unsigned long crash_low_size_default(void);
> +
> +#endif /* _X86_CRASH_CORE_H */
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 382c66d2cf71..559a5c4141db 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -474,152 +474,40 @@ static void __init memblock_x86_reserve_range_setup_data(void)
>  /*
>   * --------- Crashkernel reservation ------------------------------
>   */
> -
> -/* 16M alignment for crash kernel regions */
> -#define CRASH_ALIGN		SZ_16M
> -
> -/*
> - * Keep the crash kernel below this limit.
> - *
> - * Earlier 32-bits kernels would limit the kernel to the low 512 MB range
> - * due to mapping restrictions.
> - *
> - * 64-bit kdump kernels need to be restricted to be under 64 TB, which is
> - * the upper limit of system RAM in 4-level paging mode. Since the kdump
> - * jump could be from 5-level paging to 4-level paging, the jump will fail if
> - * the kernel is put above 64 TB, and during the 1st kernel bootup there's
> - * no good way to detect the paging mode of the target kernel which will be
> - * loaded for dumping.
> - */
> -#ifdef CONFIG_X86_32
> -# define CRASH_ADDR_LOW_MAX	SZ_512M
> -# define CRASH_ADDR_HIGH_MAX	SZ_512M
> -#else
> -# define CRASH_ADDR_LOW_MAX	SZ_4G
> -# define CRASH_ADDR_HIGH_MAX	SZ_64T
> -#endif
> -
> -static int __init reserve_crashkernel_low(void)
> +unsigned long crash_low_size_default(void)
>  {
>  #ifdef CONFIG_X86_64
> -	unsigned long long base, low_base = 0, low_size = 0;
> -	unsigned long low_mem_limit;
> -	int ret;
> -
> -	low_mem_limit = min(memblock_phys_mem_size(), CRASH_ADDR_LOW_MAX);
> -
> -	/* crashkernel=Y,low */
> -	ret = parse_crashkernel_low(boot_command_line, low_mem_limit, &low_size, &base);
> -	if (ret) {
> -		/*
> -		 * two parts from kernel/dma/swiotlb.c:
> -		 * -swiotlb size: user-specified with swiotlb= or default.
> -		 *
> -		 * -swiotlb overflow buffer: now hardcoded to 32k. We round it
> -		 * to 8M for other buffers that may need to stay low too. Also
> -		 * make sure we allocate enough extra low memory so that we
> -		 * don't run out of DMA buffers for 32-bit devices.
> -		 */
> -		low_size = max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20);
> -	} else {
> -		/* passed with crashkernel=0,low ? */
> -		if (!low_size)
> -			return 0;
> -	}
> -
> -	low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
> -	if (!low_base) {
> -		pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n",
> -		       (unsigned long)(low_size >> 20));
> -		return -ENOMEM;
> -	}
> -
> -	pr_info("Reserving %ldMB of low memory at %ldMB for crashkernel (low RAM limit: %ldMB)\n",
> -		(unsigned long)(low_size >> 20),
> -		(unsigned long)(low_base >> 20),
> -		(unsigned long)(low_mem_limit >> 20));
> -
> -	crashk_low_res.start = low_base;
> -	crashk_low_res.end   = low_base + low_size - 1;
> -	insert_resource(&iomem_resource, &crashk_low_res);
> -#endif
> +	return max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20);
> +#else
>  	return 0;
> +#endif
>  }
>  
> -static void __init reserve_crashkernel(void)
> +static void __init arch_reserve_crashkernel(void)
>  {
> -	unsigned long long crash_size, crash_base, total_mem;
> +	unsigned long long crash_base, crash_size, low_size = 0;
> +	char *cmdline = boot_command_line;
>  	bool high = false;
>  	int ret;
>  
>  	if (!IS_ENABLED(CONFIG_KEXEC_CORE))
>  		return;
>  
> -	total_mem = memblock_phys_mem_size();
> -
> -	/* crashkernel=XM */
> -	ret = parse_crashkernel(boot_command_line, total_mem,
> -				&crash_size, &crash_base, NULL, NULL);
> -	if (ret != 0 || crash_size <= 0) {
> -		/* crashkernel=X,high */
> -		ret = parse_crashkernel_high(boot_command_line, total_mem,
> -					     &crash_size, &crash_base);
> -		if (ret != 0 || crash_size <= 0)
> -			return;
> -		high = true;
> -	}
> +	ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
> +				&crash_size, &crash_base,
> +				&low_size, &high);
> +	if (ret)
> +		return;
>  
>  	if (xen_pv_domain()) {
>  		pr_info("Ignoring crashkernel for a Xen PV domain\n");
>  		return;
>  	}
>  
> -	/* 0 means: find the address automatically */
> -	if (!crash_base) {
> -		/*
> -		 * Set CRASH_ADDR_LOW_MAX upper bound for crash memory,
> -		 * crashkernel=x,high reserves memory over 4G, also allocates
> -		 * 256M extra low memory for DMA buffers and swiotlb.
> -		 * But the extra memory is not required for all machines.
> -		 * So try low memory first and fall back to high memory
> -		 * unless "crashkernel=size[KMG],high" is specified.
> -		 */
> -		if (!high)
> -			crash_base = memblock_phys_alloc_range(crash_size,
> -						CRASH_ALIGN, CRASH_ALIGN,
> -						CRASH_ADDR_LOW_MAX);
> -		if (!crash_base)
> -			crash_base = memblock_phys_alloc_range(crash_size,
> -						CRASH_ALIGN, CRASH_ALIGN,
> -						CRASH_ADDR_HIGH_MAX);
> -		if (!crash_base) {
> -			pr_info("crashkernel reservation failed - No suitable area found.\n");
> -			return;
> -		}
> -	} else {
> -		unsigned long long start;
> -
> -		start = memblock_phys_alloc_range(crash_size, SZ_1M, crash_base,
> -						  crash_base + crash_size);
> -		if (start != crash_base) {
> -			pr_info("crashkernel reservation failed - memory is in use.\n");
> -			return;
> -		}
> -	}
> -
> -	if (crash_base >= (1ULL << 32) && reserve_crashkernel_low()) {
> -		memblock_phys_free(crash_base, crash_size);
> -		return;
> -	}
> -
> -	pr_info("Reserving %ldMB of memory at %ldMB for crashkernel (System RAM: %ldMB)\n",
> -		(unsigned long)(crash_size >> 20),
> -		(unsigned long)(crash_base >> 20),
> -		(unsigned long)(total_mem >> 20));
> +	reserve_crashkernel_generic(cmdline, crash_size, crash_base,
> +				    low_size, high);
>  
> -	crashk_res.start = crash_base;
> -	crashk_res.end   = crash_base + crash_size - 1;
> -	insert_resource(&iomem_resource, &crashk_res);
> +	return;

This can be omitted.

>  }
>  
>  static struct resource standard_io_resources[] = {
> @@ -1231,7 +1119,7 @@ void __init setup_arch(char **cmdline_p)
>  	 * Reserve memory for crash kernel after SRAT is parsed so that it
>  	 * won't consume hotpluggable memory.
>  	 */
> -	reserve_crashkernel();
> +	arch_reserve_crashkernel();
>  
>  	memblock_find_dma_reserve();
>  
> 

-- 
Regards,
  Zhen Lei