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

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Dec 04, 2024 at 01:54:31PM +0100, David Hildenbrand wrote:
> 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

Who is merging this?
virtio parts:

Acked-by: Michael S. Tsirkin <mst@redhat.com>


> 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