[RFC PATCH v3 3/3] x86/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 x86 using CPA directly on the
passed direct-map address. Clear _PAGE_RW and _PAGE_DIRTY, keep alias
checks disabled like the existing direct-map _noflush helpers, 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/x86/include/asm/set_memory.h |  2 ++
 arch/x86/mm/pat/set_memory.c      | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_memory.h
index 4362c26aa992..bd3817e06052 100644
--- a/arch/x86/include/asm/set_memory.h
+++ b/arch/x86/include/asm/set_memory.h
@@ -89,6 +89,8 @@ int set_pages_rw(struct page *page, int numpages);
 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);
 
 extern int kernel_set_to_readonly;
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index d023a40a1e03..5987f4c84f6f 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2662,6 +2662,21 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
 	return __set_pages_np(page, nr);
 }
 
+int set_direct_map_ro_noflush(const void *addr, unsigned long nr_pages)
+{
+	unsigned long tempaddr = (unsigned long)addr;
+	struct cpa_data cpa = {
+		.vaddr = &tempaddr,
+		.pgd = NULL,
+		.numpages = nr_pages,
+		.mask_set = __pgprot(0),
+		.mask_clr = __pgprot(_PAGE_RW | _PAGE_DIRTY),
+		.flags = CPA_NO_CHECK_ALIAS,
+	};
+
+	return __change_page_attr_set_clr(&cpa, 1);
+}
+
 #ifdef CONFIG_DEBUG_PAGEALLOC
 void __kernel_map_pages(struct page *page, int numpages, int enable)
 {
-- 
2.49.0