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The next patch in the series with title "powerpc/crash: use generic
crashkernel reservation" enables powerpc to use generic crashkernel
reservation instead of custom implementation. This leads to exporting of
`Crash Kernel` memory to iomem_resource (/proc/iomem) via
insert_crashkernel_resources():kernel/crash_reserve.c or at another place
in the same file if HAVE_ARCH_ADD_CRASH_RES_TO_IOMEM_EARLY is set.
The add_system_ram_resources():arch/powerpc/mm/mem.c adds `System RAM` to
iomem_resource using request_resource(). This creates a conflict with
`Crash Kernel`, which is added by the generic crashkernel reservation
code. As a result, the kernel ultimately fails to add `System RAM` to
iomem_resource. Consequently, it does not appear in /proc/iomem.
There are multiple approches tried to avoid this:
1. Don't add Crash Kernel to iomem_resource:
- This has two issues.
First, it requires adding an architecture-specific hook in the
generic code. There are already two code paths to choose when to
add `Crash Kernel` to iomem_resource. This adds one more code path
to skip it.
Second, what if `Crash Kernel` is required in /proc/iomem in the
future? Many architectures do export it.
2. Don't add `System RAM` to iomem_resource by reverting commit
c40dd2f766 ("powerpc: Add System RAM to /proc/iomem"):
- It's not ideal to export `System RAM` via /proc/iomem, but since
it already done ealier and userspace tools like kdump and
kdump-utils rely on `System RAM` from /proc/iomem, removing it
will break userspace.
3. Add Crash Kernel along with System RAM to /proc/iomem:
This patch takes the third approach by updating add_system_ram_resources()
to use insert_resource() instead of the request_resource() API to add the
`System RAM` resource to iomem_resource. insert_resource() allows
inserting resources even if they overlap with existing ones. Since `Crash
Kernel` and `System RAM` resources are added to iomem_resource early in
the boot, any other conflict is not expected.
With the changes introduced here and in the next patch, "powerpc/crash:
use generic crashkernel reservation," /proc/iomem now exports `System RAM`
and `Crash Kernel` as shown below:
$ cat /proc/iomem
00000000-3ffffffff : System RAM
10000000-4fffffff : Crash kernel
The kdump script is capable of handling `System RAM` and `Crash Kernel` in
the above format. The same format is used in other architectures.
Link: https://lkml.kernel.org/r/20250131113830.925179-7-sourabhjain@linux.ibm.com
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Cc: Baoquan he <bhe@redhat.com>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.