On 09/07/2016 06:29 AM, AKASHI Takahiro wrote:
> On crash dump kernel, all the information about primary kernel's system
> memory (core image) is available in elf core header.
> The primary kernel will set aside this header with reserve_elfcorehdr()
> at boot time and inform crash dump kernel of its location via a new
> device-tree property, "linux,elfcorehdr".
>
> Please note that all other architectures use traditional "elfcorehdr="
> kernel parameter for this purpose.
>
> Then crash dump kernel will access the primary kernel's memory with
> copy_oldmem_page(), which reads one page by ioremap'ing it since it does
> not reside in linear mapping on crash dump kernel.
>
> We also need our own elfcorehdr_read() here since the header is placed
> within crash dump kernel's usable memory.
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> ---
> arch/arm64/Kconfig | 11 +++++++
> arch/arm64/kernel/Makefile | 1 +
> arch/arm64/kernel/crash_dump.c | 71 ++++++++++++++++++++++++++++++++++++++++++
> arch/arm64/mm/init.c | 54 ++++++++++++++++++++++++++++++++
> 4 files changed, 137 insertions(+)
> create mode 100644 arch/arm64/kernel/crash_dump.c
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index bc3f00f..9c15c66 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -683,6 +683,17 @@ config KEXEC
> but it is independent of the system firmware. And like a reboot
> you can start any kernel with it, not just Linux.
>
> +config CRASH_DUMP
> + bool "Build kdump crash kernel"
> + help
> + Generate crash dump after being started by kexec. This should
> + be normally only set in special crash dump kernels which are
> + loaded in the main kernel with kexec-tools into a specially
> + reserved region and then later executed after a crash by
> + kdump/kexec.
> +
> + For more details see Documentation/kdump/kdump.txt
> +
> config XEN_DOM0
> def_bool y
> depends on XEN
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 14f7b65..f1cbfc8 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -48,6 +48,7 @@ arm64-obj-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
> arm64-obj-$(CONFIG_HIBERNATION) += hibernate.o hibernate-asm.o
> arm64-obj-$(CONFIG_KEXEC) += machine_kexec.o relocate_kernel.o \
> cpu-reset.o
> +arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
>
> obj-y += $(arm64-obj-y) vdso/ probes/
> 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..bc5b932
> --- /dev/null
> +++ b/arch/arm64/kernel/crash_dump.c
> @@ -0,0 +1,71 @@
> +/*
> + * Routines for doing kexec-based kdump
> + *
> + * Copyright (C) 2014 Linaro Limited
> + * Author: AKASHI Takahiro <takahiro.akashi at 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 in a user address space
> + *
> + * 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)
> +{
> + void *vaddr;
> +
> + if (!csize)
> + return 0;
> +
> + vaddr = memremap(__pfn_to_phys(pfn), PAGE_SIZE, MEMREMAP_WB);
> + if (!vaddr)
> + return -ENOMEM;
> +
> + if (userbuf) {
> + if (copy_to_user(buf, vaddr + offset, csize)) {
> + memunmap(vaddr);
> + return -EFAULT;
> + }
> + } else {
> + memcpy(buf, vaddr + offset, csize);
> + }
> +
> + memunmap(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)
> +{
> + memcpy(buf, phys_to_virt((phys_addr_t)*ppos), count);
> + return count;
> +}
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index dd273ec..e4d9c38 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -36,6 +36,7 @@
> #include <linux/efi.h>
> #include <linux/swiotlb.h>
> #include <linux/kexec.h>
> +#include <linux/crash_dump.h>
>
> #include <asm/boot.h>
> #include <asm/fixmap.h>
> @@ -186,6 +187,57 @@ static void __init reserve_crashkernel(void)
> }
> #endif /* CONFIG_KEXEC_CORE */
>
> +#ifdef CONFIG_CRASH_DUMP
> +static int __init early_init_dt_scan_elfcorehdr(unsigned long node,
> + const char *uname, int depth, void *data)
> +{
> + const __be32 *reg;
> + int len;
> +
> + if (depth != 1 || strcmp(uname, "chosen") != 0)
> + return 0;
> +
> + reg = of_get_flat_dt_prop(node, "linux,elfcorehdr", &len);
> + if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
> + return 1;
> +
> + elfcorehdr_addr = dt_mem_next_cell(dt_root_addr_cells, ®);
> + elfcorehdr_size = dt_mem_next_cell(dt_root_size_cells, ®);
> +
> + return 1;
> +}
> +
> +/*
> + * reserve_elfcorehdr() - reserves memory for elf core header
> + *
> + * This function reserves elf core header given in "elfcorehdr=" kernel
> + * command line parameter. This region contains all the information about
> + * primary kernel's core image and is used by a dump capture kernel to
> + * access the system memory on primary kernel.
> + */
> +static void __init reserve_elfcorehdr(void)
> +{
> + of_scan_flat_dt(early_init_dt_scan_elfcorehdr, NULL);
> +
Do I get that right that we can pass crashkernel address/size through
the kernel boot parameter, but elfcorehdr can only be provided via
device tree?
Why? If there is a reason for doing so, we should fix the documentation.
Regards,
Matthias
