Hi Akashi, On 09/08/16 02:56, 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. On Seattle when I panic and boot the kdump kernel, I am unable to read the /proc/vmcore file. Instead I get: nanook at frikadeller:~$ sudo cp /proc/vmcore / [ 174.393875] Unhandled fault: synchronous external abort (0x96000210) at 0xffffff80096b6000 [ 174.402158] Internal error: : 96000210 [#1] PREEMPT SMP [ 174.407370] Modules linked in: [ 174.410417] CPU: 6 PID: 2059 Comm: cp Tainted: G S W I 4.8.0-rc1+ #4708 [ 174.417799] Hardware name: AMD Overdrive/Supercharger/Default string, BIOS ROD1002C 04/08/2016 [ 174.426396] task: ffffffc0fdec5780 task.stack: ffffffc0f34bc000 [ 174.432313] PC is at __arch_copy_to_user+0x180/0x280 [ 174.437274] LR is at copy_oldmem_page+0xac/0xf0 [ 174.441791] pc : [<ffffff800835e080>] lr : [<ffffff8008095b9c>] pstate: 20000145 [ 174.449173] sp : ffffffc0f34bfc90 [ 174.452474] x29: ffffffc0f34bfc90 x28: 0000000000000000 [ 174.457776] x27: 0000000008000000 x26: 000000000000d000 [ 174.463077] x25: 0000000000000001 x24: ffffff8008eb5000 [ 174.468378] x23: 0000000000000000 x22: ffffff80096b6000 [ 174.473679] x21: 0000000000000001 x20: 0000000030127000 [ 174.478979] x19: 0000000000001000 x18: 0000007ff7085d60 [ 174.484279] x17: 0000000000429358 x16: ffffff80081d9e88 [ 174.489579] x15: 0000007fae377590 x14: 0000000000000000 [ 174.494880] x13: 0000000000000000 x12: ffffff8008dd1000 [ 174.500180] x11: ffffff80096b6fff x10: ffffff80096b6fff [ 174.505480] x9 : 0000000040000000 x8 : ffffff8008db6000 [ 174.510781] x7 : ffffff80096b7000 x6 : 0000000030127000 [ 174.516082] x5 : 0000000030128000 x4 : 0000000000000000 [ 174.521382] x3 : 00e8000000000713 x2 : 0000000000000f80 [ 174.526682] x1 : ffffff80096b6000 x0 : 0000000030127000 [ 174.531982] [ 174.533461] Process cp (pid: 2059, stack limit = 0xffffffc0f34bc020) [ 174.848448] [<ffffff800835e080>] __arch_copy_to_user+0x180/0x280 [ 174.854448] [<ffffff8008245f34>] read_from_oldmem.part.4+0xb4/0xf4 [ 174.860615] [<ffffff8008246074>] read_vmcore+0x100/0x22c [ 174.865919] [<ffffff8008239378>] proc_reg_read+0x64/0x90 [ 174.871223] [<ffffff80081d7da8>] __vfs_read+0x28/0x108 [ 174.876348] [<ffffff80081d8ae4>] vfs_read+0x84/0x144 [ 174.881301] [<ffffff80081d9ecc>] SyS_read+0x44/0xa0 [ 174.886167] [<ffffff8008082ef0>] el0_svc_naked+0x24/0x28 [ 174.891466] Code: 00000000 00000000 00000000 00000000 (a8c12027) [ 174.897562] ---[ end trace 00801b2e35b0cd1f ]--- The offending call is: > copy_oldmem_page(0x8000000, 0x00000000385f8000, 0x1000, 0, 1) This is trying to access the bottom page of memory. From the efi memory map: > efi: 0x008000000000-0x008001e7ffff [Runtime Data |RUN| |WB|WT|WC|UC]* > efi: 0x008001e80000-0x008001ffffff [Conventional Memory| | |WB|WT|WC|UC] This page is 'Runtime Data', and marked as nomap by both the original and kdump kernels, but copy_oldmem_page() doesn't know this. In this case because we have already parsed the efi memory map again in the kdump kernel and re-marked these regions as nomap, the below hunk fixes the problem for me: =========================%<========================= diff --git a/arch/arm64/kernel/crash_dump.c b/arch/arm64/kernel/crash_dump.c index 2dc54d129be1..784d4c30b534 100644 --- a/arch/arm64/kernel/crash_dump.c +++ b/arch/arm64/kernel/crash_dump.c @@ -37,6 +37,11 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf, if (!csize) return 0; + if (memblock_is_memory(pfn << PAGE_SHIFT) && + !memblock_is_map_memory(pfn << PAGE_SHIFT)) + /* skip this nomap memory region, reserved by firmware */ + return 0; + vaddr = ioremap_cache(__pfn_to_phys(pfn), PAGE_SIZE); if (!vaddr) return -ENOMEM; =========================%<========================= With this I can copy the vmcore file, and feed it to crash to read dmesg, task list etc... This could be a deeper/wider issue, but I can't see any other users of memblock_mark_nomap(). Do you think depending on this this 're-learning' is robust enough, or should the nomap ranges be described in the vmcoreinfo elf notes? Thanks, James > diff --git a/arch/arm64/kernel/crash_dump.c b/arch/arm64/kernel/crash_dump.c > new file mode 100644 > index 0000000..2dc54d1 > --- /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_to_phys(pfn), 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; > +}