linux-kernel - [PATCH 0/3] Update crashkernel offset to allow kernel to boot on large config LPARs

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Message-Id: <20211008161552.211262-1-sourabhjain@linux.ibm.com>
Date:   Fri,  8 Oct 2021 21:45:49 +0530
From:   Sourabh Jain <sourabhjain@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     hbathini@...ux.ibm.com, mahesh@...ux.vnet.ibm.com,
        mpe@...erman.id.au, linuxppc-dev@...abs.org,
        aneesh.kumar@...ux.ibm.com
Subject: [PATCH 0/3] Update crashkernel offset to allow kernel to boot on large config LPARs

As the crashkernel reserve memory at 128MB offset in the first memory
block, it leaves less than 128MB memory to accommodate other essential
system resources that need memory reservation in the same block. This
creates kernel boot failure on large config LPARs having core count
greater than 192.

Setting the crashkernel to mid of RMA size which can be 512MB or more
instead of capping it to 128MB by default leaves enough space to allocate
memory to another system resource in the first memory block.

Now keeping the crashkernel at mid of RMA size works fine for the primary
kernel but creates boot failure for the kdump kernel when the crashekernel
reservation start offset crosses 256MB. The reason is, in the early boot
MMU feature of 1T segments support is not detected which restricts the paca
allocation for boot CPU below 256MB. When the crashkernel itself is
starting at 256MB offset, attempt to allocate paca below 256MB leads to the
kdump kernel boot failure.

Moving the detection of segment sizes before identifying the boot CPU
removes the restriction of 256MB limit for boot CPU paca allocation
which allows the kdump kernel to successfully boot and capture vmcore.

While allocating paca for boot CPU we found that there is a small window
during kernel boot where early_radix_enabled returns True even though
the radix is disabled using command-line. This leads to an invalid bolated
size calculation on which paca limit of boot CPU is dependent. Patch 0001
closes that window that by fixing the radix bit in mmu_feature.

changes in v2:
	0001: Rename the function name to update_cpu_features() as per
	      the review comment.
	0002: Fixed compilation error reported by kernel test robot.
	0003: Added comment and updated commit message

Mahesh Salgaonkar (2):
  fixup mmu_features immediately after getting cpu pa features.
  Remove 256MB limit restriction for boot cpu paca allocation

Sourabh Jain (1):
  powerpc: Set crashkernel offset to mid of RMA region

 arch/powerpc/include/asm/book3s/64/mmu.h |  2 ++
 arch/powerpc/include/asm/mmu.h           |  1 +
 arch/powerpc/kernel/prom.c               |  8 ++++++++
 arch/powerpc/kernel/rtas.c               |  4 ++++
 arch/powerpc/kexec/core.c                | 15 +++++++++++----
 arch/powerpc/mm/book3s64/hash_utils.c    |  5 ++++-
 arch/powerpc/mm/init_64.c                |  5 ++++-
 7 files changed, 34 insertions(+), 6 deletions(-)

-- 
2.31.1