Re: [PATCH v24 5/9] arm64: kdump: add kdump support

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Wed, Aug 24, 2016 at 04:44:09PM +0200, Ard Biesheuvel wrote:
> On 9 August 2016 at 03:56, AKASHI Takahiro <takahiro.akashi@linaro.org> 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@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 69c8787..9ede54b 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -682,6 +682,17 @@ 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..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@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);
> 
> Could we please use memremap() here?
> 
> > +       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);
> 
> ... and memunmap here?
> 
> ioremap_cache() is not very well defined, and memremap() has been
> introduced specifically to replace it, so I think we should use it in
> new code.

Sure. I will use memremap(MEMREMAP_WB) instead.

Thanks,
-Takahiro AKASHI

> Thanks,
> Ard.
> 
> 
> > +
> > +       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 e3771c4..bba1e39 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, &reg);
> > +       elfcorehdr_size = dt_mem_next_cell(dt_root_size_cells, &reg);
> > +
> > +       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);
> > +
> > +       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 0x%llx for elfcorehdr\n",
> > +               elfcorehdr_size >> 10, elfcorehdr_addr);
> > +}
> > +#else
> > +static void __init reserve_elfcorehdr(void)
> > +{
> > +       ;
> > +}
> > +#endif /* CONFIG_CRASH_DUMP */
> >  /*
> >   * Return the maximum physical address for ZONE_DMA (DMA_BIT_MASK(32)). It
> >   * currently assumes that for memory starting above 4G, 32-bit devices will
> > @@ -444,6 +496,8 @@ void __init arm64_memblock_init(void)
> >
> >         reserve_crashkernel();
> >
> > +       reserve_elfcorehdr();
> > +
> >         dma_contiguous_reserve(arm64_dma_phys_limit);
> >
> >         memblock_allow_resize();
> > --
> > 2.9.0
> >
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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