Subject: [PATCH v2 2/2] powerpc/fadump: opt out from freeing pages on cma activation failure

From: Hari Bathini <[email-masked]>
Date: Thu, 13 Jan 2022 01:03:40 +0530

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.

Signed-off-by: Hari Bathini <[email-masked]>
---
 arch/powerpc/kernel/fadump.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
index b7ceb041743c..82058b52e34a 100644
--- a/arch/powerpc/kernel/fadump.c
+++ b/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.
 	 */
-- 
2.34.1