Re: [PATCH 1/5] arm64: kdump: reserve memory for crash dump kernel

[Geoff Levand <geoff@infradead.org>]

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/

> 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/

> 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@linaro.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.

> + *
> + * Copyright (C) 2014 Linaro Limited
> + * Author: AKASHI Takahiro <takahiro.akashi@linaro.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/

> + *
> + * 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?

> +{
> +	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 *?

> +{
> +	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?

> +		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?

> +	/*
> +	 * 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.

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