Subject: Re: [PATCH v8 2/5] arm64: kdump: reserve crashkenel above 4G for crash dump kernel

From: Baoquan He <[email-masked]>
Date: Tue, 26 May 2020 08:59:04 +0800

On 05/21/20 at 05:38pm, Chen Zhou wrote:
> Crashkernel=X tries to reserve memory for the crash dump kernel under
> 4G. If crashkernel=X,low is specified simultaneously, reserve spcified
> size low memory for crash kdump kernel devices firstly and then reserve
> memory above 4G.

Wondering why crashkernel=,high is not introduced to arm64 to be
consistent with x86_64, to make the behaviour be the same on all
architecutres. 

> 
> Signed-off-by: Chen Zhou <[email-masked]>
> Tested-by: John Donnelly <[email-masked]>
> Tested-by: Prabhakar Kushwaha <[email-masked]>
> ---
>  arch/arm64/kernel/setup.c |  8 +++++++-
>  arch/arm64/mm/init.c      | 31 +++++++++++++++++++++++++++++--
>  2 files changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 3fd2c11c09fc..a8487e4d3e5a 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -238,7 +238,13 @@ 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" region in /proc/iomem.
> +		 * Note: the low region is renamed as Crash kernel (low).
> +		 */
> +		if (crashk_low_res.end && crashk_low_res.start >= res->start &&
> +				crashk_low_res.end <= res->end)
> +			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 e42727e3568e..71498acf0cd8 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -81,6 +81,7 @@ static void __init reserve_crashkernel(void)
>  {
>  	unsigned long long crash_base, crash_size;
>  	int ret;
> +	phys_addr_t crash_max = arm64_dma32_phys_limit;
>  
>  	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
>  				&crash_size, &crash_base);
> @@ -88,12 +89,38 @@ static void __init reserve_crashkernel(void)
>  	if (ret || !crash_size)
>  		return;
>  
> +	ret = reserve_crashkernel_low();
> +	if (!ret && crashk_low_res.end) {
> +		/*
> +		 * If crashkernel=X,low specified, there may be two regions,
> +		 * we need to make some changes as follows:
> +		 *
> +		 * 1. rename the low region as "Crash kernel (low)"
> +		 * 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)".
> +		 *
> +		 * 2. change the upper bound for crash memory
> +		 * Set MEMBLOCK_ALLOC_ACCESSIBLE upper bound for crash memory.
> +		 *
> +		 * 3. mark the low region as "nomap"
> +		 * The low region is intended to be used for crash dump kernel
> +		 * devices, just mark the low region as "nomap" simply.
> +		 */
> +		const char *rename = "Crash kernel (low)";
> +
> +		crashk_low_res.name = rename;
> +		crash_max = MEMBLOCK_ALLOC_ACCESSIBLE;
> +		memblock_mark_nomap(crashk_low_res.start,
> +				    resource_size(&crashk_low_res));
> +	}
> +
>  	crash_size = PAGE_ALIGN(crash_size);
>  
>  	if (crash_base == 0) {
>  		/* Current arm64 boot protocol requires 2MB alignment */
> -		crash_base = memblock_find_in_range(0, arm64_dma32_phys_limit,
> -				crash_size, SZ_2M);
> +		crash_base = memblock_find_in_range(0, crash_max, crash_size,
> +				SZ_2M);
>  		if (crash_base == 0) {
>  			pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>  				crash_size);
> -- 
> 2.20.1
> 
> 
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