Re: [PATCH v17 07/10] arm64: kdump: reimplement crashkernel=X

[john.p.donnelly@oracle.com]

On 12/10/21 12:55 AM, Zhen Lei wrote:
> From: Chen Zhou <chenzhou10@huawei.com>
> 
> 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.
> 
> To solve these issues, change the behavior of crashkernel=X and
> introduce crashkernel=X,[high,low]. crashkernel=X tries low allocation
> in DMA zone, 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.
> "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 <chenzhou10@huawei.com>
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> Tested-by: John Donnelly <John.p.donnelly@oracle.com>
> Tested-by: Dave Kleikamp <dave.kleikamp@oracle.com>

  Acked-by: John Donnelly <john.p.donnelly@oracle.com>

> ---
>   arch/arm64/Kconfig                     |  1 +
>   arch/arm64/include/asm/kexec.h         |  4 ++
>   arch/arm64/kernel/machine_kexec_file.c | 12 +++++-
>   arch/arm64/kernel/setup.c              | 13 +++++-
>   arch/arm64/mm/init.c                   | 59 +++++---------------------
>   5 files changed, 38 insertions(+), 51 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index c4207cf9bb17ffb..4b99efa36da3793 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -95,6 +95,7 @@ config ARM64
>   	select ARCH_WANT_FRAME_POINTERS
>   	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
>   	select ARCH_WANT_LD_ORPHAN_WARN
> +	select ARCH_WANT_RESERVE_CRASH_KERNEL if KEXEC_CORE
>   	select ARCH_WANTS_NO_INSTR
>   	select ARCH_HAS_UBSAN_SANITIZE_ALL
>   	select ARM_AMBA
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index 1b9edc69f0244ca..3bde0079925d771 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -96,6 +96,10 @@ 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
> +
>   #if defined(CONFIG_KEXEC_CORE)
>   void cpu_soft_restart(unsigned long el2_switch, unsigned long entry,
>   		      unsigned long arg0, unsigned long arg1,
> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> index 63634b4d72c158f..6f3fa059ca4e816 100644
> --- a/arch/arm64/kernel/machine_kexec_file.c
> +++ b/arch/arm64/kernel/machine_kexec_file.c
> @@ -65,10 +65,18 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
>   
>   	/* 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;
> +	}
>   
> -	if (!ret)
> -		ret =  crash_prepare_elf64_headers(cmem, true, addr, sz);
> +	ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
>   
> +out:
>   	kfree(cmem);
>   	return ret;
>   }
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index be5f85b0a24de69..4bb2e55366be64d 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -248,7 +248,18 @@ 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 be4595dc7459115..85c83e4eff2b6c4 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -36,6 +36,7 @@
>   #include <asm/fixmap.h>
>   #include <asm/kasan.h>
>   #include <asm/kernel-pgtable.h>
> +#include <asm/kexec.h>
>   #include <asm/kvm_host.h>
>   #include <asm/memory.h>
>   #include <asm/numa.h>
> @@ -64,57 +65,11 @@ EXPORT_SYMBOL(memstart_addr);
>    */
>   phys_addr_t arm64_dma_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.
> - */
> +#ifndef CONFIG_KEXEC_CORE
>   static void __init reserve_crashkernel(void)
>   {
> -	unsigned long long crash_base, crash_size;
> -	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
> -	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);
> -
> -	/* User specifies base address explicitly. */
> -	if (crash_base)
> -		crash_max = crash_base + crash_size;
> -
> -	/* Current arm64 boot protocol requires 2MB alignment */
> -	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
> -					       crash_base, crash_max);
> -	if (!crash_base) {
> -		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
> -			crash_size);
> -		return;
> -	}
> -
> -	pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
> -		crash_base, crash_base + crash_size, crash_size >> 20);
> -
> -	/*
> -	 * The crashkernel memory will be removed from the kernel linear
> -	 * map. Inform kmemleak so that it won't try to access it.
> -	 */
> -	kmemleak_ignore_phys(crash_base);
> -	crashk_res.start = crash_base;
> -	crashk_res.end = crash_base + crash_size - 1;
>   }
> -#else
> -static void __init reserve_crashkernel(void)
> -{
> -}
> -#endif /* CONFIG_KEXEC_CORE */
> +#endif
>   
>   /*
>    * Return the maximum physical address for a zone accessible by the given bits
> @@ -362,6 +317,14 @@ void __init bootmem_init(void)
>   	 * reserved, so do it here.
>   	 */
>   	reserve_crashkernel();
> +#ifdef CONFIG_KEXEC_CORE
> +	/*
> +	 * The low region is intended to be used for crash dump kernel devices,
> +	 * just mark the low region as "nomap" simply.
> +	 */
> +	if (crashk_low_res.end)
> +		memblock_mark_nomap(crashk_low_res.start, resource_size(&crashk_low_res));
> +#endif
>   
>   	memblock_dump_all();
>   }