[RFC PATCH v3 2/3] arm64/mm: add set_direct_map_ro_noflush()

[Xueyuan Chen <xueyuan.chen21@gmail.com>]

From: Xueyuan Chen <xueyuan.chen21@gmail.com>

Implement set_direct_map_ro_noflush() for arm64 with update_range_prot() on
the linear map, setting PTE_RDONLY and clearing PTE_WRITE. Keep the
existing can_set_direct_map() guard and leave TLB invalidation to the
caller.

Co-developed-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Xueyuan Chen <xueyuan.chen21@gmail.com>
---
 arch/arm64/include/asm/set_memory.h |  2 ++
 arch/arm64/mm/pageattr.c            | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/arm64/include/asm/set_memory.h b/arch/arm64/include/asm/set_memory.h
index 90f61b17275e..7083260303c3 100644
--- a/arch/arm64/include/asm/set_memory.h
+++ b/arch/arm64/include/asm/set_memory.h
@@ -14,6 +14,8 @@ int set_memory_valid(unsigned long addr, int numpages, int enable);
 int set_direct_map_invalid_noflush(struct page *page);
 int set_direct_map_default_noflush(struct page *page);
 int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid);
+int set_direct_map_ro_noflush(const void *addr, unsigned long nr_pages);
+#define set_direct_map_ro_noflush set_direct_map_ro_noflush
 bool kernel_page_present(struct page *page);
 
 int set_memory_encrypted(unsigned long addr, int numpages);
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index bbe98ac9ad8c..1a6769073558 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -365,6 +365,16 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
 	return set_memory_valid(addr, nr, valid);
 }
 
+int set_direct_map_ro_noflush(const void *addr, unsigned long nr_pages)
+{
+	if (!can_set_direct_map())
+		return 0;
+
+	return update_range_prot((unsigned long)addr, PAGE_SIZE * nr_pages,
+				 __pgprot(PTE_RDONLY),
+				 __pgprot(PTE_WRITE));
+}
+
 #ifdef CONFIG_DEBUG_PAGEALLOC
 /*
  * This is - apart from the return value - doing the same
-- 
2.49.0