On Tue, Nov 24, 2015 at 10:25:34PM +0000, Geoff Levand wrote:
> From: AKASHI Takahiro <takahiro.akashi at linaro.org>
>
> On crash dump kernel, all the information about primary kernel's core
> image is available in elf core header specified by "elfcorehdr=" boot
> parameter. reserve_elfcorehdr() will set aside the region to avoid any
> corruption by crash dump kernel.
>
> Crash dump kernel will access the system memory of primary kernel via
> copy_oldmem_page(), which reads one page by ioremap'ing it since it does
> not reside in linear mapping on crash dump kernel.
> Please note that we should add "mem=X[MG]" boot parameter to limit the
> memory size and avoid the following assertion at ioremap():
> if (WARN_ON(pfn_valid(__phys_to_pfn(phys_addr))))
> return NULL;
> when accessing any pages beyond the usable memories of crash dump kernel.
>
> We also need our own elfcorehdr_read() here since the weak definition of
> elfcorehdr_read() utilizes copy_oldmem_page() and will hit the assertion
> above on arm64.
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> ---
> arch/arm64/Kconfig | 12 +++++++
> arch/arm64/kernel/Makefile | 1 +
> arch/arm64/kernel/crash_dump.c | 71 ++++++++++++++++++++++++++++++++++++++++++
> arch/arm64/mm/init.c | 29 +++++++++++++++++
> 4 files changed, 113 insertions(+)
> create mode 100644 arch/arm64/kernel/crash_dump.c
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index c23fd77..4bac7dc 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -545,6 +545,18 @@ 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. The crash dump kernel must be compiled to a
> + memory address not used by the main kernel.
What does this even mean? How do I "compile to a memory address not used
by the main kernel"?
> diff --git a/arch/arm64/kernel/crash_dump.c b/arch/arm64/kernel/crash_dump.c
> new file mode 100644
> index 0000000..3d86c0a
> --- /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 = ioremap_cache(pfn << PAGE_SHIFT, PAGE_SIZE);
pfn_to_page
> + 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)
> +{
> + memcpy(buf, phys_to_virt((phys_addr_t)*ppos), count);
> + return count;
> +}
I know you say that we have to override this function so that we don't
hit the pfn_valid warning in ioremap, but what guarantees that the ELF
header of the crashed kernel is actually mapped in our linear mapping?
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 24f0a1c..52a1469 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -35,6 +35,7 @@
> #include <linux/efi.h>
> #include <linux/swiotlb.h>
> #include <linux/kexec.h>
> +#include <linux/crash_dump.h>
>
> #include <asm/fixmap.h>
> #include <asm/memory.h>
> @@ -116,6 +117,31 @@ static void __init reserve_crashkernel(void)
> }
> #endif /* CONFIG_KEXEC */
>
> +#ifdef CONFIG_CRASH_DUMP
> +/*
> + * 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)
> +{
> + if (!elfcorehdr_size)
> + return;
> +
> + if (memblock_is_region_reserved(elfcorehdr_addr, elfcorehdr_size)) {
> + pr_warn("elfcorehdr is overlapped\n");
> + return;
> + }
> +
> + memblock_reserve(elfcorehdr_addr, elfcorehdr_size);
> +
> + pr_info("Reserving %lldKB of memory at %lldMB for elfcorehdr\n",
> + elfcorehdr_size >> 10, elfcorehdr_addr >> 20);
I'd have thought it would be more useful to print the address as an
address rather than a size.
> +}
Similar #else trick here.
Will
