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powerpc/64/kdump: Limit kdump base to 512MB

Mamatha Inamdar requested to merge mainamdar/centos-stream-9:2127026 into main

Bugzilla: https://bugzilla.redhat.com/2127026

Build Info: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=48588712

Tested: Verified Brew build test kernel RPMs and confirmed issue is resovled

commit bd7dc90e52e8db7ee0f38c51bc9047bafb54fe43 Author: Hari Bathini hbathini@linux.ibm.com Date: Mon Sep 12 12:20:31 2022 +0530

powerpc/64/kdump: Limit kdump base to 512MB

Since commit e641eb03ab2b0 ("powerpc: Fix up the kdump base cap to
128M") memory for kdump kernel has been reserved at an offset of 128MB.
This held up well for a long time before running into boot failure on
LPARs having a lot of cores. Commit 7c5ed82b800d8 ("powerpc: Set
crashkernel offset to mid of RMA region") fixed this boot failure by
moving the offset to mid of RMA region. This change meant the offset is
either 256MB or 512MB on LPARs as ppc64_rma_size was 512MB or 1024MB
owing to commit 103a8542cb35b ("powerpc/book3s64/ radix: Fix boot
failure with large amount of guest memory").

But ppc64_rma_size can be larger as well with newer f/w. So, limit
crashkernel reservation offset to 512MB to avoid running into boot
failures during kdump kernel boot, due to RTAS or other allocation
restrictions.

Also, while here, use SZ_128M instead of opening coding it.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Tested-by: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220912065031.57416-1-hbathini@linux.ibm.com

Signed-off-by: Mamatha Inamdar minamdar@redhat.com

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