Re: [PATCH v1 00/11] fs/proc/vmcore: kdump support for virtio-mem on s390

[Baoquan He <bhe@redhat.com>]

On 10/25/24 at 05:11pm, David Hildenbrand wrote:
> This is based on "[PATCH v3 0/7] virtio-mem: s390 support" [1], which adds
> virtio-mem support on s390.
> 
> 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
> crash kernel must detect memory ranges of the crashed/panicked 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
                                       ~~~~~~~~~~~
                                       Is it 1st kernel or 2nd kernel?
Usually we call the 1st kernel as panicked kernel, crashed kernel, the
2nd kernel as kdump kernel. 
> 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().

Do you mean on s390 virtio-mem memory region will be detected and added
to vmcore in kdump kernel when virtio-mem driver is initialized? Not
sure if I understand it correctly.

> 
> 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.
> 
> Note that makedumfile is shaky with v6.12-rcX, I made the "obvious" things
> (e.g., free page detection) work again while testing as documented in [2].
> 
> Creating the dumps using makedumpfile seems to work fine, and the
> dump regions (PT_LOAD) are as expected. I yet have to check in more detail
> if the created dumps are good (IOW, the right memory was dumped, but it
> looks like makedumpfile reads the right memory when interpreting the
> kernel data structures, which is promising).
> 
> Patch #1 -- #6 are vmcore preparations and cleanups
> Patch #7 adds the infrastructure for drivers to report device RAM
> Patch #8 + #9 are virtio-mem preparations
> Patch #10 implements virtio-mem support to report device RAM
> Patch #11 activates it for s390, implementing a new function to fill
>           PT_LOAD entry for device RAM
> 
> [1] https://lkml.kernel.org/r/20241025141453.1210600-1-david@redhat.com
> [2] https://github.com/makedumpfile/makedumpfile/issues/16
> 
> 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 (11):
>   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 after the vmcore was
>     opened
>   fs/proc/vmcore: move vmcore definitions from kcore.h to crash_dump.h
>   fs/proc/vmcore: factor out allocating a vmcore memory node
>   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/Kconfig        |   1 +
>  drivers/virtio/virtio_mem.c   | 103 +++++++++++++-
>  fs/proc/Kconfig               |  25 ++++
>  fs/proc/vmcore.c              | 258 +++++++++++++++++++++++++---------
>  include/linux/crash_dump.h    |  47 +++++++
>  include/linux/kcore.h         |  13 --
>  8 files changed, 396 insertions(+), 91 deletions(-)
> 
> -- 
> 2.46.1
>