Re: [PATCH v14 08/11] arm64: kdump: reimplement crashkernel=X
From: chenzhou
Date: Fri Feb 26 2021 - 05:44:44 EST
On 2021年2月26日 18:31, chenzhou wrote:
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On 2021年2月25日 0:04, Catalin Marinas wrote:
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> On Sat, Jan 30, 2021 at 03:10:22PM +0800, Chen Zhou wrote:
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>> There are following issues in arm64 kdump:
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>> 1. We use crashkernel=X to reserve crashkernel below 4G, which
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>> will fail when there is no enough low memory.
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>> 2. If reserving crashkernel above 4G, in this case, crash dump
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>> kernel will boot failure because there is no low memory available
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>> for allocation.
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>>
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>> To solve these issues, change the behavior of crashkernel=X and
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>> introduce crashkernel=X,[high,low]. crashkernel=X tries low allocation
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>> in DMA zone, and fall back to high allocation if it fails.
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>> We can also use "crashkernel=X,high" to select a region above DMA zone,
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>> which also tries to allocate at least 256M in DMA zone automatically.
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>> "crashkernel=Y,low" can be used to allocate specified size low memory.
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>>
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>> Another minor change, there may be two regions reserved for crash
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>> dump kernel, in order to distinct from the high region and make no
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>> effect to the use of existing kexec-tools, rename the low region as
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>> "Crash kernel (low)".
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> 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?
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Yes.
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> 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?
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Suffix "low" only appear if a high region is additionally reserved.
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>> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
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>> index 3f6ecae0bc68..f0caed0cb5e1 100644
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>> --- a/arch/arm64/include/asm/kexec.h
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>> +++ b/arch/arm64/include/asm/kexec.h
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>> @@ -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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>>
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>> +#ifdef CONFIG_KEXEC_CORE
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>> +extern void __init reserve_crashkernel(void);
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>> +#endif
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> Why not have this in some generic header?
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>
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>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
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>> index c18aacde8bb0..69c592c546de 100644
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>> --- a/arch/arm64/kernel/setup.c
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>> +++ b/arch/arm64/kernel/setup.c
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>> @@ -238,7 +238,18 @@ static void __init request_standard_resources(void)
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>> kernel_data.end <= res->end)
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>> request_resource(res, &kernel_data);
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>> #ifdef CONFIG_KEXEC_CORE
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>> - /* Userspace will find "Crash kernel" region in /proc/iomem. */
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>> + /*
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>> + * Userspace will find "Crash kernel" or "Crash kernel (low)"
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>> + * region in /proc/iomem.
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>> + * In order to distinct from the high region and make no effect
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>> + * to the use of existing kexec-tools, rename the low region as
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>> + * "Crash kernel (low)".
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>> + */
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>> + if (crashk_low_res.end && crashk_low_res.start >= res->start &&
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>> + crashk_low_res.end <= res->end) {
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>> + crashk_low_res.name = "Crash kernel (low)";
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>> + request_resource(res, &crashk_low_res);
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>> + }
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>> if (crashk_res.end && crashk_res.start >= res->start &&
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>> crashk_res.end <= res->end)
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>> request_resource(res, &crashk_res);
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> 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
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> would not get a renamed low reservation (as long as they don't change
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> the kernel cmdline).
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>
>
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
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>> index 912f64f505f7..d20f5c444ebf 100644
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>> --- a/arch/arm64/mm/init.c
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>> +++ b/arch/arm64/mm/init.c
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>> @@ -35,6 +35,7 @@
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>> #include <asm/fixmap.h>
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>> #include <asm/kasan.h>
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>> #include <asm/kernel-pgtable.h>
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>> +#include <asm/kexec.h>
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>> #include <asm/memory.h>
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>> #include <asm/numa.h>
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>> #include <asm/sections.h>
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>> @@ -61,66 +62,11 @@ EXPORT_SYMBOL(memstart_addr);
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>> */
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>> phys_addr_t arm64_dma_phys_limit __ro_after_init;
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>>
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>> -#ifdef CONFIG_KEXEC_CORE
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>> -/*
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>> - * reserve_crashkernel() - reserves memory for crash kernel
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>> - *
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>> - * This function reserves memory area given in "crashkernel=" kernel command
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>> - * line parameter. The memory reserved is used by dump capture kernel when
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>> - * primary kernel is crashing.
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>> - */
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>> +#ifndef CONFIG_KEXEC_CORE
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>> static void __init reserve_crashkernel(void)
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>> {
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> [...]
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>> }
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>> +#endif
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> Can we not have the dummy reserve_crashkernel() in the generic code as
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> well and avoid the #ifndef here?
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You mean put the dummy reserve_crashkernel() and the relate function declaration in some generic header?
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>
Baoquan also mentioned about this.
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Now all the arch that support kdump have the dummy reserve_crashkernel() and
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function declaration, such as arm/arm64/ppc/s390..
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>
But currently different arch may have different CONFIG and different function declaration about this,
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for example,
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>
for s390,
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static void __init reserve_crashkernel(void)
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{
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#ifdef CONFIG_CRASH_DUMP
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...
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#endif
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}
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for ppc,
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#ifdef CONFIG_KEXEC_CORE
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extern void reserve_crashkernel(void);
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#else
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static inline void reserve_crashkernel(void) { ; }
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#endif
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>
If we move these to generic header we need think about:
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1. the related config in different arch
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2. function declaration(static/non static)
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>
As Baoquan said in patch 9, how about leave with it for now and i try to solve this later?
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>
>> #ifdef CONFIG_CRASH_DUMP
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>> static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
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>> @@ -446,6 +392,14 @@ void __init bootmem_init(void)
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>> * reserved, so do it here.
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>> */
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>> reserve_crashkernel();
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>> +#ifdef CONFIG_KEXEC_CORE
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>> + /*
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>> + * The low region is intended to be used for crash dump kernel devices,
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>> + * just mark the low region as "nomap" simply.
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>> + */
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>> + if (crashk_low_res.end)
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>> + memblock_mark_nomap(crashk_low_res.start, resource_size(&crashk_low_res));
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>> +#endif
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> Do we do something similar for crashk_res?
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Not. In the primary kernel(production kernel), we need to use crashk_res memory for crash kernel
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elf core header, initrd...
Sorry, missed one comma after crash kernel.
Not. In the primary kernel(production kernel), we need to use crashk_res memory for crash kernel,
elf core header, initrd and so on.
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>
Different with this, the crashk_low_res is only for crash dump kernel devices.
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> Also, I can see we call crash_exclude_mem_range() only for crashk_res.
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> Do we need to do this for crashk_low_res as well?
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You are right, i missed about this. Will do in next version.
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Thanks,
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Chen Zhou