linux-kernel - Re: [PATCH 1/4] x86: kdump: move reserve_crashkernel_low() into kexec

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Date:   Wed, 5 Jun 2019 17:29:21 +0100
From:   James Morse <james.morse@....com>
To:     Chen Zhou <chenzhou10@...wei.com>
Cc:     catalin.marinas@....com, will.deacon@....com,
        akpm@...ux-foundation.org, ard.biesheuvel@...aro.org,
        rppt@...ux.ibm.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, ebiederm@...ssion.com, horms@...ge.net.au,
        takahiro.akashi@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        linux-mm@...ck.org, wangkefeng.wang@...wei.com
Subject: Re: [PATCH 1/4] x86: kdump: move reserve_crashkernel_low() into
 kexec_core.c

Hello,

On 07/05/2019 04:50, Chen Zhou wrote:
> In preparation for supporting reserving crashkernel above 4G
> in arm64 as x86_64 does, move reserve_crashkernel_low() into
> kexec/kexec_core.c.


> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 905dae8..9ee33b6 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -463,59 +460,6 @@ static void __init memblock_x86_reserve_range_setup_data(void)
>  # define CRASH_ADDR_HIGH_MAX	MAXMEM
>  #endif
>  
> -static int __init reserve_crashkernel_low(void)
> -{
> -#ifdef CONFIG_X86_64

The behaviour of this #ifdef has disappeared, won't 32bit x86 now try and reserve a chunk
of unnecessary 'low' memory?

[...]


> @@ -579,9 +523,13 @@ static void __init reserve_crashkernel(void)
>  		return;
>  	}
>  
> -	if (crash_base >= (1ULL << 32) && reserve_crashkernel_low()) {
> -		memblock_free(crash_base, crash_size);
> -		return;
> +	if (crash_base >= (1ULL << 32)) {
> +		if (reserve_crashkernel_low()) {
> +			memblock_free(crash_base, crash_size);
> +			return;
> +		}
> +
> +		insert_resource(&iomem_resource, &crashk_low_res);


Previously reserve_crashkernel_low() was #ifdefed to do nothing if !CONFIG_X86_64, I don't
see how 32bit is skipping this reservation...


>  	}
>  
>  	pr_info("Reserving %ldMB of memory at %ldMB for crashkernel (System RAM: %ldMB)\n",
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index b9b1bc5..096ad63 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -63,6 +63,10 @@
>  
>  #define KEXEC_CORE_NOTE_NAME	CRASH_CORE_NOTE_NAME
>  
> +#ifndef CRASH_ALIGN
> +#define CRASH_ALIGN SZ_128M
> +#endif

Why 128M? Wouldn't we rather each architecture tells us its minimum alignment?


> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index d714044..3492abd 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -39,6 +39,8 @@
>  #include <linux/compiler.h>
>  #include <linux/hugetlb.h>
>  #include <linux/frame.h>
> +#include <linux/memblock.h>
> +#include <linux/swiotlb.h>
>  
>  #include <asm/page.h>
>  #include <asm/sections.h>
> @@ -96,6 +98,60 @@ int kexec_crash_loaded(void)
>  }
>  EXPORT_SYMBOL_GPL(kexec_crash_loaded);
>  
> +int __init reserve_crashkernel_low(void)
> +{
> +	unsigned long long base, low_base = 0, low_size = 0;
> +	unsigned long total_low_mem;
> +	int ret;
> +
> +	total_low_mem = memblock_mem_size(1UL << (32 - PAGE_SHIFT));
> +
> +	/* crashkernel=Y,low */
> +	ret = parse_crashkernel_low(boot_command_line, total_low_mem,
> +			&low_size, &base);
> +	if (ret) {
> +		/*
> +		 * two parts from lib/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),

SZ_8M?

> +				256UL << 20);

SZ_256M?


> +	} else {
> +		/* passed with crashkernel=0,low ? */
> +		if (!low_size)
> +			return 0;
> +	}
> +
> +	low_base = memblock_find_in_range(0, 1ULL << 32, low_size, CRASH_ALIGN);
> +	if (!low_base) {
> +		pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n",
> +		       (unsigned long)(low_size >> 20));
> +		return -ENOMEM;
> +	}
> +
> +	ret = memblock_reserve(low_base, low_size);
> +	if (ret) {
> +		pr_err("%s: Error reserving crashkernel low memblock.\n",
> +				__func__);
> +		return ret;
> +	}
> +
> +	pr_info("Reserving %ldMB of low memory at %ldMB for crashkernel (System low RAM: %ldMB)\n",
> +		(unsigned long)(low_size >> 20),
> +		(unsigned long)(low_base >> 20),
> +		(unsigned long)(total_low_mem >> 20));
> +
> +	crashk_low_res.start = low_base;
> +	crashk_low_res.end   = low_base + low_size - 1;
> +
> +	return 0;
> +}


Thanks,

James