[PATCH v2 00/12] fs/proc/vmcore: kdump support for virtio-mem on s390

[David Hildenbrand]

The only "different than everything else" thing about virtio-mem on s390
is kdump: The crash (2nd) kernel allocates+prepares the elfcore hdr
during fs_init()->vmcore_init()->elfcorehdr_alloc(). Consequently, the
kdump kernel must detect memory ranges of the crashed kernel to
include via PT_LOAD in the vmcore.

On other architectures, all RAM regions (boot + hotplugged) can easily be
observed on the old (to crash) kernel (e.g., using /proc/iomem) to create
the elfcore hdr.

On s390, information about "ordinary" memory (heh, "storage") can be
obtained by querying the hypervisor/ultravisor via SCLP/diag260, and
that information is stored early during boot in the "physmem" memblock
data structure.

But virtio-mem memory is always detected by as device driver, which is
usually build as a module. So in the crash kernel, this memory can only be
properly detected once the virtio-mem driver started up.

The virtio-mem driver already supports the "kdump mode", where it won't
hotplug any memory but instead queries the device to implement the
pfn_is_ram() callback, to avoid reading unplugged memory holes when reading
the vmcore.

With this series, if the virtio-mem driver is included in the kdump
initrd -- which dracut already takes care of under Fedora/RHEL -- it will
now detect the device RAM ranges on s390 once it probes the devices, to add
them to the vmcore using the same callback mechanism we already have for
pfn_is_ram().

To add these device RAM ranges to the vmcore ("patch the vmcore"), we will
add new PT_LOAD entries that describe these memory ranges, and update
all offsets vmcore size so it is all consistent.

My testing when creating+analyzing crash dumps with hotplugged virtio-mem
memory (incl. holes) did not reveal any surprises.

Patch #1 -- #7 are vmcore preparations and cleanups
Patch #8 adds the infrastructure for drivers to report device RAM
Patch #9 + #10 are virtio-mem preparations
Patch #11 implements virtio-mem support to report device RAM
Patch #12 activates it for s390, implementing a new function to fill
          PT_LOAD entry for device RAM

v1 -> v2:
* "fs/proc/vmcore: convert vmcore_cb_lock into vmcore_mutex"
 -> Extend patch description
* "fs/proc/vmcore: replace vmcoredd_mutex by vmcore_mutex"
 -> Extend patch description
* "fs/proc/vmcore: disallow vmcore modifications while the vmcore is open"
 -> Disallow modifications only if it is currently open, but warn if it
    was already open and got closed again.
 -> Track vmcore_open vs. vmcore_opened
 -> Extend patch description
* "fs/proc/vmcore: prefix all pr_* with "vmcore:""
 -> Added
* "fs/proc/vmcore: move vmcore definitions out if kcore.h"
 -> Call it "vmcore_range"
 -> Place vmcoredd_node into vmcore.c
 -> Adjust patch subject + description
* "fs/proc/vmcore: factor out allocating a vmcore range and adding it to a
   list"
 -> Adjust to "vmcore_range"
* "fs/proc/vmcore: factor out freeing a list of vmcore ranges"
 -> Adjust to "vmcore_range"
* "fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM to detect device RAM
   ranges in 2nd kernel"
 -> Drop PROVIDE_PROC_VMCORE_DEVICE_RAM for now
 -> Simplify Kconfig a bit
 -> Drop "Kdump:" from warnings/errors
 -> Perform Elf64 check first
 -> Add regions also if the vmcore was opened, but got closed again. But
    warn in any case, because it is unexpected.
 -> Adjust patch description
* "virtio-mem: support CONFIG_PROC_VMCORE_DEVICE_RAM"
 -> "depends on VIRTIO_MEM" for PROC_VMCORE_DEVICE_RAM


Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Cc: "Eugenio Pérez" <eperezma@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Thomas Huth <thuth@xxxxxxxxxx>
Cc: Cornelia Huck <cohuck@xxxxxxxxxx>
Cc: Janosch Frank <frankja@xxxxxxxxxxxxx>
Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Cc: Eric Farman <farman@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

David Hildenbrand (12):
  fs/proc/vmcore: convert vmcore_cb_lock into vmcore_mutex
  fs/proc/vmcore: replace vmcoredd_mutex by vmcore_mutex
  fs/proc/vmcore: disallow vmcore modifications while the vmcore is open
  fs/proc/vmcore: prefix all pr_* with "vmcore:"
  fs/proc/vmcore: move vmcore definitions out of kcore.h
  fs/proc/vmcore: factor out allocating a vmcore range and adding it to
    a list
  fs/proc/vmcore: factor out freeing a list of vmcore ranges
  fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM to detect device RAM
    ranges in 2nd kernel
  virtio-mem: mark device ready before registering callbacks in kdump
    mode
  virtio-mem: remember usable region size
  virtio-mem: support CONFIG_PROC_VMCORE_DEVICE_RAM
  s390/kdump: virtio-mem kdump support (CONFIG_PROC_VMCORE_DEVICE_RAM)

 arch/s390/Kconfig             |   1 +
 arch/s390/kernel/crash_dump.c |  39 ++++-
 drivers/virtio/virtio_mem.c   | 103 ++++++++++++-
 fs/proc/Kconfig               |  19 +++
 fs/proc/vmcore.c              | 283 ++++++++++++++++++++++++++--------
 include/linux/crash_dump.h    |  41 +++++
 include/linux/kcore.h         |  13 --
 7 files changed, 407 insertions(+), 92 deletions(-)


base-commit: feffde684ac29a3b7aec82d2df850fbdbdee55e4
-- 
2.47.1