[PATCH 2/2] powerpc/strict_rwx: fixup region splitting

[Balbir Singh]

We were aggressive with splitting regions and missed the case
when _stext and __init_begin completely overlap addr and addr+mapping.

This patch fixes that case and allows us to keep the largest possible
mapping through the overlap. The patch also simplies the check
into a function

Fixes: 7614ff3 ("powerpc/mm/radix: Implement STRICT_RWX/mark_rodata_ro() for Radix")

Signed-off-by: Balbir Singh <bsingharora at gmail.com>
---
 arch/powerpc/mm/pgtable-radix.c | 39 ++++++++++++++++++++++++++++-----------
 1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
index c2a2b46..ea0da3b 100644
--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -210,17 +210,36 @@ static inline void __meminit print_mapping(unsigned long start,
 	pr_info("Mapped 0x%016lx-0x%016lx with %s pages\n", start, end, buf);
 }
 
+static inline int __meminit
+should_split_mapping_size(unsigned long addr, unsigned long mapping_size)
+{
+#ifdef CONFIG_STRICT_KERNEL_RWX
+	/*
+	 * If addr, addr+mapping overlap the text region and
+	 * _stext and __init_begin end up lying between
+	 * addr, addr+mapping split the mapping size down
+	 * further
+	 */
+	if ((addr < __pa_symbol(__init_begin)) &&
+		(addr + mapping_size) > __pa_symbol(_stext)) {
+
+		if (((addr + mapping_size) <= __pa_symbol(__init_begin)) &&
+			(addr >= __pa_symbol(_stext)))
+			return 0;
+
+		return 1;
+	}
+#endif
+	return 0;
+}
+
+
 static int __meminit create_physical_mapping(unsigned long start,
 					     unsigned long end)
 {
 	unsigned long vaddr, addr, mapping_size = 0;
 	pgprot_t prot;
 	unsigned long max_mapping_size;
-#ifdef CONFIG_STRICT_KERNEL_RWX
-	int split_text_mapping = 1;
-#else
-	int split_text_mapping = 0;
-#endif
 
 	start = _ALIGN_UP(start, PAGE_SIZE);
 	for (addr = start; addr < end; addr += mapping_size) {
@@ -242,16 +261,14 @@ static int __meminit create_physical_mapping(unsigned long start,
 		else
 			mapping_size = PAGE_SIZE;
 
-		if (split_text_mapping && (mapping_size == PUD_SIZE) &&
-			(addr <= __pa_symbol(__init_begin)) &&
-			(addr + mapping_size) >= __pa_symbol(_stext)) {
+		if ((mapping_size == PUD_SIZE) &&
+			should_split_mapping_size(addr, mapping_size)) {
 			max_mapping_size = PMD_SIZE;
 			goto retry;
 		}
 
-		if (split_text_mapping && (mapping_size == PMD_SIZE) &&
-		    (addr <= __pa_symbol(__init_begin)) &&
-		    (addr + mapping_size) >= __pa_symbol(_stext))
+		if ((mapping_size == PMD_SIZE) &&
+			should_split_mapping_size(addr, mapping_size))
 			mapping_size = PAGE_SIZE;
 
 		if (mapping_size != previous_size) {
-- 
2.9.5