+ powerpc-fadump-opt-out-from-freeing-pages-on-cma-activation-failure.patch added to -mm tree

+ powerpc-fadump-opt-out-from-freeing-pages-on-cma-activation-failure.patch added to -mm tree

[akpm]

The patch titled
     Subject: powerpc/fadump: opt out from freeing pages on cma activation failure
has been added to the -mm tree.  Its filename is
     powerpc-fadump-opt-out-from-freeing-pages-on-cma-activation-failure.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/powerpc-fadump-opt-out-from-freeing-pages-on-cma-activation-failure.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/powerpc-fadump-opt-out-from-freeing-pages-on-cma-activation-failure.patch

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------------------------------------------------------
From: Hari Bathini <hbathini@linux.ibm.com>
Subject: powerpc/fadump: opt out from freeing pages on cma activation failure

With commit a4e92ce8e4c8 ("powerpc/fadump: Reservationless firmware
assisted dump"), Linux kernel's Contiguous Memory Allocator (CMA) based
reservation was introduced in fadump.  That change was aimed at using CMA
to let applications utilize the memory reserved for fadump while blocking
it from being used for kernel pages.  The assumption was, even if CMA
activation fails for whatever reason, the memory still remains reserved to
avoid it from being used for kernel pages.  But commit 072355c1cf2d
("mm/cma: expose all pages to the buddy if activation of an area fails")
breaks this assumption as it started exposing all pages to buddy allocator
on CMA activation failure.  It led to warning messages like below while
running crash-utility on vmcore of a kernel having above two commits:

  crash: seek error: kernel virtual address: <from reserved region>

To fix this problem, opt out from exposing pages to buddy allocator on CMA
activation failure for fadump reserved memory.

Link: https://lkml.kernel.org/r/20220117075246.36072-3-hbathini@linux.ibm.com
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/powerpc/kernel/fadump.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/arch/powerpc/kernel/fadump.c~powerpc-fadump-opt-out-from-freeing-pages-on-cma-activation-failure
+++ a/arch/powerpc/kernel/fadump.c
@@ -113,6 +113,12 @@ static int __init fadump_cma_init(void)
 	}
 
 	/*
+	 *  If CMA activation fails, keep the pages reserved, instead of
+	 *  exposing them to buddy allocator. Same as 'fadump=nocma' case.
+	 */
+	cma_reserve_pages_on_error(fadump_cma);
+
+	/*
 	 * So we now have successfully initialized cma area for fadump.
 	 */
 	pr_info("Initialized 0x%lx bytes cma area at %ldMB from 0x%lx "
_

Patches currently in -mm which might be from hbathini@linux.ibm.com are

mm-cma-provide-option-to-opt-out-from-exposing-pages-on-activation-failure.patch
powerpc-fadump-opt-out-from-freeing-pages-on-cma-activation-failure.patch