Re: [PATCH v14 08/11] arm64: kdump: reimplement crashkernel=X
From: chenzhou
Date: Fri Feb 26 2021 - 05:35:09 EST
On 2021年2月25日 0:04, Catalin Marinas wrote:
>
On Sat, Jan 30, 2021 at 03:10:22PM +0800, 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.
>
>
>
> 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)".
>
I think we discussed this but I don't remember the conclusion. Is this
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only renamed conditionally so that we don't break current kexec-tools?
Yes.
>
>
IOW, assuming that the full crashkernel region is reserved below 4GB,
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does the "(low)" suffix still appear or it's only if a high region is
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additionally reserved?
Suffix "low" only appear if a high region is additionally reserved.
>
>
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
>
> index 3f6ecae0bc68..f0caed0cb5e1 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) {}
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> static inline void crash_post_resume(void) {}
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> #endif
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>
>
> +#ifdef CONFIG_KEXEC_CORE
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> +extern void __init reserve_crashkernel(void);
>
> +#endif
>
Why not have this in some generic header?
>
>
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
>
> index c18aacde8bb0..69c592c546de 100644
>
> --- a/arch/arm64/kernel/setup.c
>
> +++ b/arch/arm64/kernel/setup.c
>
> @@ -238,7 +238,18 @@ static void __init request_standard_resources(void)
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> kernel_data.end <= res->end)
>
> request_resource(res, &kernel_data);
>
> #ifdef CONFIG_KEXEC_CORE
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> - /* Userspace will find "Crash kernel" region in /proc/iomem. */
>
> + /*
>
> + * Userspace will find "Crash kernel" or "Crash kernel (low)"
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> + * 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);
>
> + }
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> if (crashk_res.end && crashk_res.start >= res->start &&
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> crashk_res.end <= res->end)
>
> request_resource(res, &crashk_res);
>
My reading of the new generic reserve_crashkernel() is that
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crashk_low_res will only be populated if crask_res is above 4GB. If
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that's correct, I'm fine with the renaming here since current systems
>
would not get a renamed low reservation (as long as they don't change
>
the kernel cmdline).
>
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>
> index 912f64f505f7..d20f5c444ebf 100644
>
> --- a/arch/arm64/mm/init.c
>
> +++ b/arch/arm64/mm/init.c
>
> @@ -35,6 +35,7 @@
>
> #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>
>
> @@ -61,66 +62,11 @@ EXPORT_SYMBOL(memstart_addr);
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> */
>
> 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
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> - * primary kernel is crashing.
>
> - */
>
> +#ifndef CONFIG_KEXEC_CORE
>
> static void __init reserve_crashkernel(void)
>
> {
>
[...]
>
> }
>
> +#endif
>
Can we not have the dummy reserve_crashkernel() in the generic code as
>
well and avoid the #ifndef here?
You mean put the dummy reserve_crashkernel() and the relate function declaration in some generic header?
Baoquan also mentioned about this.
Now all the arch that support kdump have the dummy reserve_crashkernel() and
function declaration, such as arm/arm64/ppc/s390..
But currently different arch may have different CONFIG and different function declaration about this,
for example,
for s390,
static void __init reserve_crashkernel(void)
{
#ifdef CONFIG_CRASH_DUMP
...
#endif
}
for ppc,
#ifdef CONFIG_KEXEC_CORE
extern void reserve_crashkernel(void);
#else
static inline void reserve_crashkernel(void) { ; }
#endif
If we move these to generic header we need think about:
1. the related config in different arch
2. function declaration(static/non static)
As Baoquan said in patch 9, how about leave with it for now and i try to solve this later?
>
>
> #ifdef CONFIG_CRASH_DUMP
>
> static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
>
> @@ -446,6 +392,14 @@ void __init bootmem_init(void)
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> * 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
>
Do we do something similar for crashk_res?
Not. In the primary kernel(production kernel), we need to use crashk_res memory for crash kernel
elf core header, initrd...
Different with this, the crashk_low_res is only for crash dump kernel devices.
>
>
Also, I can see we call crash_exclude_mem_range() only for crashk_res.
>
Do we need to do this for crashk_low_res as well?
You are right, i missed about this. Will do in next version.
Thanks,
Chen Zhou
>