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

David Hildenbrand
2024-12-04T12:54:51Z

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@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: "Eugenio Pérez" <eperezma@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Thomas Huth <thuth@redhat.com>
Cc: Cornelia Huck <cohuck@redhat.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Eric Farman <farman@linux.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>

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