powerpc/fadump: opt out from freeing pages on cma activation failure

With commit a4e92ce ("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 072355c
("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/[email protected]
Signed-off-by: Hari Bathini <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Cc: Mahesh Salgaonkar <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Sourabh Jain <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: hbathini

arch/powerpc/kernel/fadump.c

@@ -112,6 +112,12 @@ static int __init fadump_cma_init(void)
 		return 1;
 	}
 
+	/*
+	 *  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.
 	 */