Subject: Re: [PATCH v13 6/8] arm64: kdump: reimplement crashkernel=X

From: Baoquan He <[email-masked]>
Date: Wed, 11 Nov 2020 09:59:26 +0800

On 10/31/20 at 03:44pm, Chen Zhou wrote:
> There are following issues in arm64 kdump:
> 1. We use crashkernel=X to reserve crashkernel below 4G, which
> will fail when there is no enough low memory.
> 2. If reserving crashkernel above 4G, in this case, crash dump
> kernel will boot failure because there is no low memory available
> for allocation.
> 3. Since commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32"),
> if the memory reserved for crash dump kernel falled in ZONE_DMA32,
> the devices in crash dump kernel need to use ZONE_DMA will alloc
> fail.
> 
> To solve these issues, change the behavior of crashkernel=X and
> introduce crashkernel=X,[high,low]. crashkernel=X tries low allocation
> in DMA zone or DMA32 zone if CONFIG_ZONE_DMA is disabled, and fall back
> to high allocation if it fails.
> We can also use "crashkernel=X,high" to select a region above DMA zone,
> which also tries to allocate at least 256M in DMA zone automatically
> (or the DMA32 zone if CONFIG_ZONE_DMA is disabled).
> "crashkernel=Y,low" can be used to allocate specified size low memory.
> 
> Another minor change, there may be two regions reserved for crash
> dump kernel, in order to distinct from the high region and make no
> effect to the use of existing kexec-tools, rename the low region as
> "Crash kernel (low)".
> 
> Signed-off-by: Chen Zhou <[email-masked]>
> Tested-by: John Donnelly <[email-masked]>
> ---
>  arch/arm64/include/asm/kexec.h |  9 +++++
>  arch/arm64/kernel/setup.c      | 13 +++++++-
>  arch/arm64/mm/init.c           | 60 ++--------------------------------
>  arch/arm64/mm/mmu.c            |  4 +++
>  kernel/crash_core.c            |  8 +++--
>  5 files changed, 34 insertions(+), 60 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index 402d208265a3..79909ae5e22e 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -28,7 +28,12 @@
>  /* 2M alignment for crash kernel regions */
>  #define CRASH_ALIGN	SZ_2M
>  
> +#ifdef CONFIG_ZONE_DMA
> +#define CRASH_ADDR_LOW_MAX	arm64_dma_phys_limit
> +#else
>  #define CRASH_ADDR_LOW_MAX	arm64_dma32_phys_limit
> +#endif
> +
>  #define CRASH_ADDR_HIGH_MAX	MEMBLOCK_ALLOC_ACCESSIBLE
>  
>  #ifndef __ASSEMBLY__
> @@ -96,6 +101,10 @@ static inline void crash_prepare_suspend(void) {}
>  static inline void crash_post_resume(void) {}
>  #endif
>  
> +#ifdef CONFIG_KEXEC_CORE
> +extern void __init reserve_crashkernel(void);
> +#endif
> +
>  #ifdef CONFIG_KEXEC_FILE
>  #define ARCH_HAS_KIMAGE_ARCH
>  
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 133257ffd859..6aff30de8f47 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -238,7 +238,18 @@ static void __init request_standard_resources(void)
>  		    kernel_data.end <= res->end)
>  			request_resource(res, &kernel_data);
>  #ifdef CONFIG_KEXEC_CORE
> -		/* Userspace will find "Crash kernel" region in /proc/iomem. */
> +		/*
> +		 * Userspace will find "Crash kernel" or "Crash kernel (low)"
> +		 * region in /proc/iomem.
> +		 * In order to distinct from the high region and make no effect
> +		 * to the use of existing kexec-tools, rename the low region as
> +		 * "Crash kernel (low)".
> +		 */
> +		if (crashk_low_res.end && crashk_low_res.start >= res->start &&
> +				crashk_low_res.end <= res->end) {
> +			crashk_low_res.name = "Crash kernel (low)";
> +			request_resource(res, &crashk_low_res);
> +		}
>  		if (crashk_res.end && crashk_res.start >= res->start &&
>  		    crashk_res.end <= res->end)
>  			request_resource(res, &crashk_res);
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index a07fd8e1f926..888c4f7eadc3 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -34,6 +34,7 @@
>  #include <asm/fixmap.h>
>  #include <asm/kasan.h>
>  #include <asm/kernel-pgtable.h>
> +#include <asm/kexec.h>
>  #include <asm/memory.h>
>  #include <asm/numa.h>
>  #include <asm/sections.h>
> @@ -62,66 +63,11 @@ EXPORT_SYMBOL(memstart_addr);
>  phys_addr_t arm64_dma_phys_limit __ro_after_init;
>  phys_addr_t arm64_dma32_phys_limit __ro_after_init;
>  
> -#ifdef CONFIG_KEXEC_CORE
> -/*
> - * reserve_crashkernel() - reserves memory for crash kernel
> - *
> - * This function reserves memory area given in "crashkernel=" kernel command
> - * line parameter. The memory reserved is used by dump capture kernel when
> - * primary kernel is crashing.
> - */
> -static void __init reserve_crashkernel(void)
> -{
> -	unsigned long long crash_base, crash_size;
> -	int ret;
> -
> -	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> -				&crash_size, &crash_base);
> -	/* no crashkernel= or invalid value specified */
> -	if (ret || !crash_size)
> -		return;
> -
> -	crash_size = PAGE_ALIGN(crash_size);
> -
> -	if (crash_base == 0) {
> -		/* Current arm64 boot protocol requires 2MB alignment */
> -		crash_base = memblock_find_in_range(CRASH_ALIGN, CRASH_ADDR_LOW_MAX,
> -				crash_size, CRASH_ALIGN);
> -		if (crash_base == 0) {
> -			pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
> -				crash_size);
> -			return;
> -		}
> -	} else {
> -		/* User specifies base address explicitly. */
> -		if (!memblock_is_region_memory(crash_base, crash_size)) {
> -			pr_warn("cannot reserve crashkernel: region is not memory\n");
> -			return;
> -		}
> -
> -		if (memblock_is_region_reserved(crash_base, crash_size)) {
> -			pr_warn("cannot reserve crashkernel: region overlaps reserved memory\n");
> -			return;
> -		}
> -
> -		if (!IS_ALIGNED(crash_base, CRASH_ALIGN)) {
> -			pr_warn("cannot reserve crashkernel: base address is not 2MB aligned\n");
> -			return;
> -		}
> -	}
> -	memblock_reserve(crash_base, crash_size);
> -
> -	pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
> -		crash_base, crash_base + crash_size, crash_size >> 20);
> -
> -	crashk_res.start = crash_base;
> -	crashk_res.end = crash_base + crash_size - 1;
> -}
> -#else
> +#ifndef CONFIG_KEXEC_CORE
>  static void __init reserve_crashkernel(void)
>  {
>  }
> -#endif /* CONFIG_KEXEC_CORE */
> +#endif
>  
>  #ifdef CONFIG_CRASH_DUMP
>  static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 1c0f3e02f731..c55cee290bbb 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -488,6 +488,10 @@ static void __init map_mem(pgd_t *pgdp)
>  	 */
>  	memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
>  #ifdef CONFIG_KEXEC_CORE
> +	if (crashk_low_res.end)
> +		memblock_mark_nomap(crashk_low_res.start,
> +				    resource_size(&crashk_low_res));
> +
>  	if (crashk_res.end)
>  		memblock_mark_nomap(crashk_res.start,
>  				    resource_size(&crashk_res));
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index d39892bdb9ae..cdef7d8c91a6 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -321,7 +321,7 @@ int __init parse_crashkernel_low(char *cmdline,
>  
>  int __init reserve_crashkernel_low(void)
>  {
> -#ifdef CONFIG_X86_64
> +#if defined(CONFIG_X86_64) || defined(CONFIG_ARM64)

Not very sure if a CONFIG_64BIT checking is better.

>  	unsigned long long base, low_base = 0, low_size = 0;
>  	unsigned long low_mem_limit;
>  	int ret;
> @@ -362,12 +362,14 @@ int __init reserve_crashkernel_low(void)
>  
>  	crashk_low_res.start = low_base;
>  	crashk_low_res.end   = low_base + low_size - 1;
> +#ifdef CONFIG_X86_64
>  	insert_resource(&iomem_resource, &crashk_low_res);
> +#endif
>  #endif
>  	return 0;
>  }
>  
> -#ifdef CONFIG_X86
> +#if defined(CONFIG_X86) || defined(CONFIG_ARM64)

Should we make this weak default so that we can remove the ARCH config?

>  #ifdef CONFIG_KEXEC_CORE
>  /*
>   * reserve_crashkernel() - reserves memory for crash kernel
> @@ -453,7 +455,9 @@ void __init reserve_crashkernel(void)
>  
>  	crashk_res.start = crash_base;
>  	crashk_res.end   = crash_base + crash_size - 1;
> +#ifdef CONFIG_X86
>  	insert_resource(&iomem_resource, &crashk_res);
> +#endif
>  }
>  #endif /* CONFIG_KEXEC_CORE */
>  #endif
> -- 
> 2.20.1
> 
> 
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> 

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