Date:	Mon, 30 Mar 2015 11:35:56 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Geoff Levand <geoff@...radead.org>
CC:	catalin.marinas@....com, will.deacon@....com, vgoyal@...hat.com,
	hbabus@...ibm.com, broonie@...nel.org, david.griego@...aro.org,
	kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] arm64: kdump: reserve memory for crash dump kernel

Thank you, Geoff.

On 03/27/2015 01:43 PM, Geoff Levand wrote:
> Hi Takahiro,
>
> On Thu, 2015-03-26 at 17:28 +0900, AKASHI Takahiro wrote:
>> On system kernel, the memory region used by crash dump kernel must be
>> specified by "crashkernel=X@Y" boot parameter. reserve_crashkernel()
>> will allocate the region in "System RAM" and reserve it for later use.
>>
>> On crash dump kernel, memory region information in system kernel is
>> described in a specific region specified by "elfcorehdr=X@Y" boot parameter.
>> reserve_elfcorehdr() will set aside the region to avoid data destruction
>> by the kernel.
>>
>> Crash dump kernel will access memory regions in system kernel via
>> copy_oldmem_page(), which reads a page with ioremap'ing it assuming that
>
> s/page with/page by/

Fix it.

>> such pages are not part of main memory of crash dump kernel.
>> This is true under non-UEFI environment because kexec-tools modifies
>> a device tree adding "usablemem" attributes to memory sections.
>> Under UEFI, however, this is not true because UEFI remove memory sections
>> in a device tree and export all the memory regions, even though they belong
>> to system kernel.
>>
>> So we should add "mem=X[MG]" boot parameter to limit the meory size and
>
> s/meory/memory/

Fix it.

>> avoid hitting the following assertion in ioremap():
>> 	if (WARN_ON(pfn_valid(__phys_to_pfn(phys_addr))))
>> 		return NULL;
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
>> ---
>>   arch/arm64/kernel/Makefile     |    1 +
>>   arch/arm64/kernel/crash_dump.c |   71 ++++++++++++++++++++++++++++++++++++
>>   arch/arm64/kernel/setup.c      |   78 ++++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 150 insertions(+)
>>   create mode 100644 arch/arm64/kernel/crash_dump.c
>>
>> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
>> index da9a7ee..3c24d4e 100644
>> --- a/arch/arm64/kernel/Makefile
>> +++ b/arch/arm64/kernel/Makefile
>> @@ -36,6 +36,7 @@ arm64-obj-$(CONFIG_EFI)			+= efi.o efi-stub.o efi-entry.o
>>   arm64-obj-$(CONFIG_PCI)			+= pci.o
>>   arm64-obj-$(CONFIG_ARMV8_DEPRECATED)	+= armv8_deprecated.o
>>   arm64-obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
>> +arm64-obj-$(CONFIG_CRASH_DUMP)		+= crash_dump.o
>>
>>   obj-y					+= $(arm64-obj-y) vdso/
>>   obj-m					+= $(arm64-obj-m)
>> diff --git a/arch/arm64/kernel/crash_dump.c b/arch/arm64/kernel/crash_dump.c
>> new file mode 100644
>> index 0000000..dd31b2e
>> --- /dev/null
>> +++ b/arch/arm64/kernel/crash_dump.c
>> @@ -0,0 +1,71 @@
>> +/*
>> + * arch/arm64/kernel/crash_dump.c
>
> I would recommend against adding paths in source files.  It often
> happens that files with paths are moved, but the file comments are not
> updated.

Yeah, will fix it.

>> + *
>> + * Copyright (C) 2014 Linaro Limited
>> + * Author: AKASHI Takahiro <takahiro.akashi@...aro.org>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#include <linux/crash_dump.h>
>> +#include <linux/errno.h>
>> +#include <linux/io.h>
>> +#include <linux/memblock.h>
>> +#include <linux/uaccess.h>
>> +#include <asm/memory.h>
>> +
>> +/**
>> + * copy_oldmem_page() - copy one page from old kernel memory
>> + * @pfn: page frame number to be copied
>> + * @buf: buffer where the copied page is placed
>> + * @csize: number of bytes to copy
>> + * @offset: offset in bytes into the page
>> + * @userbuf: if set, @buf is int he user address space
>
> s/is int he user/is a user/

Fix it. Sorry for bunch of typos.

>> + *
>> + * This function copies one page from old kernel memory into buffer pointed by
>> + * @buf. If @buf is in userspace, set @userbuf to %1. Returns number of bytes
>> + * copied or negative error in case of failure.
>> + */
>> +ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
>> +			 size_t csize, unsigned long offset,
>> +			 int userbuf)
>
> Since userbuf is a binary flag, I think type bool would be better.
> Change the comments from 'set' and '1' to 'true'.
>
> Should offset be type size_t?

No. The prototype is already there in include/linux/crash_dump.h.

>> +{
>> +	void *vaddr;
>> +
>> +	if (!csize)
>> +		return 0;
>> +
>> +	vaddr = ioremap(pfn << PAGE_SHIFT, PAGE_SIZE);
>> +	if (!vaddr)
>> +		return -ENOMEM;
>> +
>> +	if (userbuf) {
>> +		if (copy_to_user(buf, vaddr + offset, csize)) {
>> +			iounmap(vaddr);
>> +			return -EFAULT;
>> +		}
>> +	} else {
>> +		memcpy(buf, vaddr + offset, csize);
>> +	}
>> +
>> +	iounmap(vaddr);
>> +
>> +	return csize;
>> +}
>> +
>> +/**
>> + * elfcorehdr_read - read from ELF core header
>> + * @buf: buffer where the data is placed
>> + * @csize: number of bytes to read
>> + * @ppos: address in the memory
>> + *
>> + * This function reads @count bytes from elf core header which exists
>> + * on crash dump kernel's memory.
>> + */
>> +ssize_t elfcorehdr_read(char *buf, size_t count, u64 *ppos)
>
> Should ppos be type phys_addr_t *?

No. The prototype is already there in include/linux/crash_dump.h.

>> +{
>> +	memcpy(buf, phys_to_virt((phys_addr_t)*ppos), count);
>> +	return count;
>> +}
>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
>> index e8420f6..daaed93 100644
>> --- a/arch/arm64/kernel/setup.c
>> +++ b/arch/arm64/kernel/setup.c
>> @@ -323,6 +323,69 @@ static void __init setup_machine_fdt(phys_addr_t dt_phys)
>>   	dump_stack_set_arch_desc("%s (DT)", of_flat_dt_get_machine_name());
>>   }
>>
>> +#ifdef CONFIG_KEXEC
>> +/*
>> + * 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 a dump capture kernel when
>> + * primary kernel is crashing.
>> + */
>> +static void __init reserve_crashkernel(void)
>> +{
>> +	unsigned long long crash_size, crash_base;
>> +	int ret;
>> +
>> +	/* use ULONG_MAX since we don't know system memory size here. */
>> +	ret = parse_crashkernel(boot_command_line, ULONG_MAX,
>> +				&crash_size, &crash_base);
>> +	if (ret)
>> +		return;
>> +
>> +	ret = memblock_reserve(crash_base, crash_size);
>> +	if (ret < 0) {
>> +		pr_warn("crashkernel reservation failed - memory is in use (0x%lx)\n",
>> +			(unsigned long)crash_base);
>
> Can we use 0x%llx here and below and avoid these casts?

Fix it.

>> +		return;
>> +	}
>> +
>> +	pr_info("Reserving %ldMB of memory at %ldMB for crashkernel\n",
>> +		(unsigned long)(crash_size >> 20),
>> +		(unsigned long)(crash_base >> 20));
>> +
>> +	crashk_res.start = crash_base;
>> +	crashk_res.end = crash_base + crash_size - 1;
>> +}
>> +#endif /* CONFIG_KEXEC */
>> +
>> +#ifdef CONFIG_CRASH_DUMP
>> +/*
>> + * reserve_elfcorehdr() - reserves memory for elf core header
>> + *
>> + * This function reserves memory area given in "elfcorehdr=" kernel command
>> + * line parameter. The memory reserved is used by a dump capture kernel to
>> + * identify the memory used by primary kernel.
>> + */
>> +static void __init reserve_elfcorehdr(void)
>> +{
>> +	int ret;
>> +
>> +	if (!elfcorehdr_size)
>> +		return;
>> +
>> +	ret = memblock_reserve(elfcorehdr_addr, elfcorehdr_size);
>> +	if (ret < 0) {
>> +		pr_warn("elfcorehdr reservation failed - memory is in use (0x%lx)\n",
>> +			(unsigned long)elfcorehdr_addr);
>> +		return;
>> +	}
>> +
>> +	pr_info("Reserving %ldKB of memory at %ldMB for elfcorehdr\n",
>> +		(unsigned long)(elfcorehdr_size >> 10),
>> +		(unsigned long)(elfcorehdr_addr >> 20));
>> +}
>> +#endif /* CONFIG_CRASH_DUMP */
>> +
>>   static void __init request_standard_resources(void)
>>   {
>>   	struct memblock_region *region;
>> @@ -378,10 +441,25 @@ void __init setup_arch(char **cmdline_p)
>>   	local_async_enable();
>>
>>   	efi_init();
>
> Maybe have a blank line here?

Add one.

>> +	/*
>> +	 * reserve_crashkernel() and reserver_elfcorehdr() must be called
>
> s/reserver_elfcorehdr/reserve_elfcorehdr/
>
>> +	 * before arm64_bootmem_init() because dma_contiguous_reserve()
>> +	 * may conflict with those regions.
>> +	 */
>> +#ifdef CONFIG_KEXEC
>> +	reserve_crashkernel();
>> +#endif
>> +#ifdef CONFIG_CRASH_DUMP
>> +	reserve_elfcorehdr();
>> +#endif
>>   	arm64_memblock_init();
>>
>>   	paging_init();
>>   	request_standard_resources();
>> +#ifdef CONFIG_KEXEC
>> +	/* kexec-tool will detect the region with /proc/iomem */
>
> There are more kexec user programs than kexec-tools, so I think
> something like 'user space tools' would be better.

Sure, fix it.

-Takahiro AKASHI

>> +	insert_resource(&iomem_resource, &crashk_res);
>> +#endif
>>
>>   	early_ioremap_reset();
>>
>
>
>
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