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    Subject[RFC PATCH 0/4 V2] introduce: livedump
    Changes in V2:
    - A little more comments are added.
    - Operation using tools/livedump/livedump is simpliefied.
    - Previous 5 patches are arranged to 4 patches.
    ([3/5] and [4/5] are merged)
    - The patchset is rebased onto v3.4.
    - crash-6.0.6 is required (which was 6.0.1 previously).

    The following series introduces the new memory dumping mechanism Live Dump,
    which let users obtain a consistent memory dump without stopping a running

    Such a mechanism is useful especially in the case where very important
    systems are consolidated onto a single machine via virtualization.
    Assuming a KVM host runs multiple important VMs on it and one of them
    fails, the other VMs have to keep running. However, at the same time, an
    administrator may want to obtain memory dump of not only the failed guest
    but also the host because possibly the cause of failture is not in the
    guest but in the host or the hardware under it.

    Live Dump is based on Copy-on-write technique. Basically processing is
    performed in the following order.
    (1) Suspends processing of all CPUs.
    (2) Makes pages (which you want to dump) read-only.
    (3) Resumes all CPUs
    (4) On page fault, dumps a page including a fault address.
    (5) Finally, dumps the rest of pages that are not updated.

    Currently, Live Dump is just a simple prototype and it has many
    limitations. I list the important ones below.
    (1) It write-protects only kernel's straight mapping areas. Therefore
    memory updates from vmap areas and user space don't cause page fault.
    Pages corresponding to these areas are not consistently dumped.
    (2) It supports only x86-64 architecture.
    (3) It can only handle 4K pages. As we know, most pages in kernel space are
    mapped via 2M or 1G large page mapping. Therefore, the current
    implementation of Live Dump splits all large pages into 4K pages before
    setting up write protection.
    (4) It allocates about 50% of physical RAM to store dumped pages. Currently
    Live Dump saves all dumped data on memory once, and after that a user
    becomes able to use the dumped data. Live Dump itself has no feature to
    save dumped data onto a disk or any other storage device.

    This series consists of 4 patches.

    Ths 1st patch adds notifier-call-chain in do_page_fault. This is the only
    modification against the existing code path of the upstream kernel.

    The 2nd patch introduces "livedump" misc device.

    The 3rd patch introduces feature of write protection management. This
    enables users to turn on write protection on kernel space and to install a
    hook function that is called every time page fault occurs on each protected

    The last patch introduces memory dumping feature. This patch installs the
    function to dump content of the protected page on page fault. At the same
    time, it lets users to access the dumped data via the misc device

    ***How to test***
    To test this patch, you have to apply the attached patch to the source code
    of crash[1]. This patch can be applied to the version 6.0.6 of crash. In
    addition to this, you have to configure your kernel to turn on


    At first, kick the script tools/livedump/livedump as follows.
    # livedump dump

    At this point, all memory image has been saved (also on memory). Then you
    can analyze the image by kicking the patched crash as follows.
    # crash /dev/livedump /boot/ /boot/vmlinux.o

    By the following command, you can release all resources of livedump.
    # livedump release


    YOSHIDA Masanori (4):
    livedump: Add memory dumping functionality
    livedump: Add write protection management
    livedump: Add the new misc device "livedump"
    livedump: Add notifier-call-chain into do_page_fault

    arch/x86/Kconfig | 29 ++
    arch/x86/include/asm/traps.h | 2
    arch/x86/include/asm/wrprotect.h | 47 +++
    arch/x86/mm/Makefile | 2
    arch/x86/mm/fault.c | 7
    arch/x86/mm/wrprotect.c | 618 ++++++++++++++++++++++++++++++++++++++
    kernel/Makefile | 1
    kernel/livedump-memdump.c | 237 +++++++++++++++
    kernel/livedump-memdump.h | 45 +++
    kernel/livedump.c | 129 ++++++++
    tools/livedump/livedump | 28 ++
    11 files changed, 1145 insertions(+), 0 deletions(-)
    create mode 100644 arch/x86/include/asm/wrprotect.h
    create mode 100644 arch/x86/mm/wrprotect.c
    create mode 100644 kernel/livedump-memdump.c
    create mode 100644 kernel/livedump-memdump.h
    create mode 100644 kernel/livedump.c
    create mode 100755 tools/livedump/livedump

    diff --git a/filesys.c b/filesys.c
    index 5c45a8f..80f5918 100755
    --- a/filesys.c
    +++ b/filesys.c
    @@ -167,6 +167,7 @@ memory_source_init(void)

    if (!STREQ(pc->live_memsrc, "/dev/mem") &&
    + !STREQ(pc->live_memsrc, "/dev/livedump") &&
    STREQ(pc->live_memsrc, pc->memory_device)) {
    if (memory_driver_init())
    @@ -187,6 +188,9 @@ memory_source_init(void)
    } else
    pc->flags |= MFD_RDWR;
    + } else if (STREQ(pc->live_memsrc, "/dev/livedump")) {
    + if ((pc->mfd = open("/dev/livedump", O_RDONLY)) < 0)
    + error(FATAL, "/dev/livedump: %s\n", strerror(errno));
    } else if (STREQ(pc->live_memsrc, "/proc/kcore")) {
    if ((pc->mfd = open("/proc/kcore", O_RDONLY)) < 0)
    error(FATAL, "/proc/kcore: %s\n",
    diff --git a/main.c b/main.c
    index 5a5e19c..8628cde 100755
    --- a/main.c
    +++ b/main.c
    @@ -436,6 +436,19 @@ main(int argc, char **argv)
    pc->writemem = write_dev_mem;
    pc->live_memsrc = argv[optind];

    + } else if (STREQ(argv[optind], "/dev/livedump")) {
    + if (pc->flags & MEMORY_SOURCES) {
    + error(INFO,
    + "too many dumpfile arguments\n");
    + program_usage(SHORT_FORM);
    + }
    + pc->flags |= DEVMEM;
    + pc->dumpfile = NULL;
    + pc->readmem = read_dev_mem;
    + pc->writemem = write_dev_mem;
    + pc->live_memsrc = argv[optind];
    + pc->program_pid = 1;
    } else if (is_proc_kcore(argv[optind], KCORE_LOCAL)) {
    if (pc->flags & MEMORY_SOURCES) {
     \ /
      Last update: 2012-05-25 11:41    [W:0.030 / U:340.100 seconds]
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