[RFC PATCH v2 3/3] x86/mm: make pages read-only in the direct map

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

Implement arch_make_pages_readonly() for x86. Make the corresponding
direct-map range read-only so unexpected writes fault instead of
corrupting shared contents.

Reject highmem pages because they have no permanent direct-map address.
Treat the set_memory_ro() update as best effort. If it fails, leave the
mapping unchanged.

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/x86/mm/init.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index fb67217fddcd..ff0a7003eaeb 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -3,6 +3,7 @@
 #include <linux/ioport.h>
 #include <linux/swap.h>
 #include <linux/memblock.h>
+#include <linux/mm.h>
 #include <linux/swapfile.h>
 #include <linux/swapops.h>
 #include <linux/kmemleak.h>
@@ -38,6 +39,14 @@
 
 #include "mm_internal.h"
 
+bool arch_make_pages_readonly(struct page *page, int nr_pages)
+{
+	if (PageHighMem(page))
+		return false;
+
+	return !set_memory_ro((unsigned long)page_address(page), nr_pages);
+}
+
 /*
  * Tables translating between page_cache_type_t and pte encoding.
  *
-- 
2.47.3