[PATCH v3 2/2] mm/memblock: only mark/clear KHO scratch memory when needed

[Usama Arif]

The scratch memory for kexec handover is used to bootstrap the
kexec'ed kernel. Only the 1st 1MB is used as scratch, and its a
hack to get around limitations with KHO. It is only needed when
CONFIG_KEXEC_HANDOVER is enabled and only if it is a KHO boot
(both checked by is_kho_boot). Add check to prevent marking a KHO
scratch region unless needed.

Fixes: a2daf83e10378 ("x86/e820: temporarily enable KHO scratch for memory below 1M")
Reported-by: Vlad Poenaru <thevlad@xxxxxxxx>
Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx>
Reviewed-by: Pratyush Yadav <pratyush@xxxxxxxxxx>
---
 mm/memblock.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 8b13d5c28922a..913cf322eb89a 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -20,8 +20,8 @@
 
 #ifdef CONFIG_KEXEC_HANDOVER
 #include <linux/libfdt.h>
-#include <linux/kexec_handover.h>
 #endif /* CONFIG_KEXEC_HANDOVER */
+#include <linux/kexec_handover.h>
 
 #include <asm/sections.h>
 #include <linux/io.h>
@@ -1126,8 +1126,10 @@ int __init_memblock memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t
  */
 __init int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size)
 {
-	return memblock_setclr_flag(&memblock.memory, base, size, 1,
-				    MEMBLOCK_KHO_SCRATCH);
+	if (is_kho_boot())
+		return memblock_setclr_flag(&memblock.memory, base, size, 1,
+					    MEMBLOCK_KHO_SCRATCH);
+	return 0;
 }
 
 /**
@@ -1140,8 +1142,10 @@ __init int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size)
  */
 __init int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size)
 {
-	return memblock_setclr_flag(&memblock.memory, base, size, 0,
-				    MEMBLOCK_KHO_SCRATCH);
+	if (is_kho_boot())
+		return memblock_setclr_flag(&memblock.memory, base, size, 0,
+					    MEMBLOCK_KHO_SCRATCH);
+	return 0;
 }
 
 static bool should_skip_region(struct memblock_type *type,
-- 
2.47.3