The patch titled
Subject: powerpc: insert System RAM resource to prevent crashkernel conflict
has been added to the -mm mm-nonmm-unstable branch. Its filename is
powerpc-insert-system-ram-resource-to-prevent-crashkernel-conflict.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/powerpc-insert-system-ram-resource-to-prevent-crashkernel-conflict.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
Subject: powerpc: insert System RAM resource to prevent crashkernel conflict
Date: Fri, 31 Jan 2025 17:08:29 +0530
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
c40dd2f766440 ("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@xxxxxxxxxxxxx
Signed-off-by: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
Cc: Baoquan he <bhe@xxxxxxxxxx>
Cc: Hari Bathini <hbathini@xxxxxxxxxxxxx>
Cc: Madhavan Srinivasan <maddy@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/mm/mem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/powerpc/mm/mem.c~powerpc-insert-system-ram-resource-to-prevent-crashkernel-conflict
+++ a/arch/powerpc/mm/mem.c
@@ -376,7 +376,7 @@ static int __init add_system_ram_resourc
*/
res->end = end - 1;
res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
- WARN_ON(request_resource(&iomem_resource, res) < 0);
+ WARN_ON(insert_resource(&iomem_resource, res) < 0);
}
}
_
Patches currently in -mm which might be from sourabhjain@xxxxxxxxxxxxx are
kexec-initialize-elf-lowest-address-to-ulong_max.patch
crash-remove-an-unused-argument-from-reserve_crashkernel_generic.patch
crash-let-arch-decide-usable-memory-range-in-reserved-area.patch
powerpc-crash-use-generic-apis-to-locate-memory-hole-for-kdump.patch
powerpc-crash-preserve-user-specified-memory-limit.patch
powerpc-insert-system-ram-resource-to-prevent-crashkernel-conflict.patch
powerpc-crash-use-generic-crashkernel-reservation.patch
