On Tue, Nov 24, 2015 at 10:25:34PM +0000, Geoff Levand wrote: > From: AKASHI Takahiro <[email protected]> > > 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 <[email protected]> > --- > 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 <[email protected]> > + * > + * 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 _______________________________________________ kexec mailing list [email protected] http://lists.infradead.org/mailman/listinfo/kexec
