[PATCH v2] ppc64/kdump: Limit kdump base to 512MB

[Hari Bathini]

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 at linux.ibm.com>
---

Changes in V2:
* Updated the changelog for clarity.
* Used SZ_512M instead of open coding as suggested by Christophe.
* Used SZ_128M instead of open coding 128MB.

 arch/powerpc/kexec/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
index cf84bfe9e27e..de64c7962991 100644
--- a/arch/powerpc/kexec/core.c
+++ b/arch/powerpc/kexec/core.c
@@ -136,7 +136,7 @@ void __init reserve_crashkernel(void)
 #ifdef CONFIG_PPC64
 		/*
 		 * On the LPAR platform place the crash kernel to mid of
-		 * RMA size (512MB or more) to ensure the crash kernel
+		 * RMA size (max. of 512MB) to ensure the crash kernel
 		 * gets enough space to place itself and some stack to be
 		 * in the first segment. At the same time normal kernel
 		 * also get enough space to allocate memory for essential
@@ -144,9 +144,9 @@ void __init reserve_crashkernel(void)
 		 * kernel starts at 128MB offset on other platforms.
 		 */
 		if (firmware_has_feature(FW_FEATURE_LPAR))
-			crashk_res.start = ppc64_rma_size / 2;
+			crashk_res.start = min_t(u64, ppc64_rma_size / 2, SZ_512M);
 		else
-			crashk_res.start = min(0x8000000ULL, (ppc64_rma_size / 2));
+			crashk_res.start = min_t(u64, ppc64_rma_size / 2, SZ_128M);
 #else
 		crashk_res.start = KDUMP_KERNELBASE;
 #endif
-- 
2.37.3