[PATCH v7 2/4] mm: Introduce memblock_isolate_memory

[Alexandre Ghiti <alexghiti@rivosinc.com>]

This function allows to split a region in memblock.memory and will be
useful when setting up the linear mapping with STRICT_KERNEL_RWX: it
allows to isolate the kernel text/rodata and then avoid to map those
regions with a PUD/P4D/PGD.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 include/linux/memblock.h |  1 +
 mm/memblock.c            | 22 +++++++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 50ad19662a32..2f7ef97c0da7 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -125,6 +125,7 @@ int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
 int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
 int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
 int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
+int memblock_isolate_memory(phys_addr_t base, phys_addr_t size);
 
 void memblock_free_all(void);
 void memblock_free(void *ptr, size_t size);
diff --git a/mm/memblock.c b/mm/memblock.c
index 25fd0626a9e7..d8cf1c9eccf0 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -753,7 +753,8 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
 	int idx;
 	struct memblock_region *rgn;
 
-	*start_rgn = *end_rgn = 0;
+	if (start_rgn && end_rgn)
+		*start_rgn = *end_rgn = 0;
 
 	if (!size)
 		return 0;
@@ -795,6 +796,9 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
 					       memblock_get_region_node(rgn),
 					       rgn->flags);
 		} else {
+			if (!end_rgn || !start_rgn)
+				continue;
+
 			/* @rgn is fully contained, record it */
 			if (!*end_rgn)
 				*start_rgn = idx;
@@ -805,6 +809,22 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
 	return 0;
 }
 
+/**
+ * memblock_isolate_memory - isolate given range from memblock.memory
+ * @base: base of range to isolate
+ * @size: size of range to isolate
+ *
+ * Call memblock_isolate_range on memblock.memory to isolate the given range.
+ *
+ * Return:
+ * 0 on success, -errno on failure.
+ */
+
+int __init_memblock memblock_isolate_memory(phys_addr_t base, phys_addr_t size)
+{
+	return memblock_isolate_range(&memblock.memory, base, size, NULL, NULL);
+}
+
 static int __init_memblock memblock_remove_range(struct memblock_type *type,
 					  phys_addr_t base, phys_addr_t size)
 {
-- 
2.37.2