[PATCH v2 2/8] arm64: Introduce can_set_direct_map_range()

[Vincent Donnefort]

For systems where can_set_direct_map() is false, it is still possible
that a subregion of the direct map can be modified if it is mapped at
the last-level. Add an implementation for can_set_direct_map_range(). It
falls back to a page table walk to verify the mapping level if
can_set_direct_map() is false.

Signed-off-by: Vincent Donnefort <vdonnefort at google.com>
---
 arch/arm64/include/asm/set_memory.h |  3 ++
 arch/arm64/mm/pageattr.c            | 50 +++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/arch/arm64/include/asm/set_memory.h b/arch/arm64/include/asm/set_memory.h
index 0091ba12200e..80bb94a340fd 100644
--- a/arch/arm64/include/asm/set_memory.h
+++ b/arch/arm64/include/asm/set_memory.h
@@ -9,6 +9,9 @@
 bool can_set_direct_map(void);
 #define can_set_direct_map can_set_direct_map
 
+bool can_set_direct_map_range(struct page *page, unsigned long numpages);
+#define can_set_direct_map_range can_set_direct_map_range
+
 int set_memory_valid(unsigned long addr, int numpages, int enable);
 
 int set_direct_map_invalid_noflush(struct page *page, unsigned int numpages);
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 132938b32eb1..5fcdb292905f 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -102,6 +102,56 @@ bool can_set_direct_map(void)
 		arm64_kfence_can_set_direct_map() || is_realm_world();
 }
 
+static int can_set_direct_map_pud_entry(pud_t *pud, unsigned long addr,
+					unsigned long next, struct mm_walk *walk)
+{
+	if (pud_leaf(pudp_get(pud)))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int can_set_direct_map_pmd_entry(pmd_t *pmd, unsigned long addr,
+					unsigned long next, struct mm_walk *walk)
+{
+	if (pmd_leaf(pmdp_get(pmd)))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int can_set_direct_map_pte_hole(unsigned long addr, unsigned long next,
+				       int depth, struct mm_walk *walk)
+{
+	return -EINVAL;
+}
+
+static const struct mm_walk_ops can_set_direct_map_ops = {
+	.pud_entry	= can_set_direct_map_pud_entry,
+	.pmd_entry	= can_set_direct_map_pmd_entry,
+	.pte_hole	= can_set_direct_map_pte_hole,
+};
+
+bool can_set_direct_map_range(struct page *page, unsigned long numpages)
+{
+	unsigned long addr = (unsigned long)page_address(page);
+	unsigned long end = addr + numpages * PAGE_SIZE;
+
+	if (can_set_direct_map())
+		return true;
+
+	if (!numpages)
+		return false;
+
+	/*
+	 * If !can_set_direct_map() then no one can split blocks and it is safe
+	 * to walk the page-table lockless.
+	 */
+	return !walk_kernel_page_table_range_lockless(addr, end,
+						      &can_set_direct_map_ops,
+						      NULL, NULL);
+}
+
 static int update_range_prot(unsigned long start, unsigned long size,
 			     pgprot_t set_mask, pgprot_t clear_mask)
 {
-- 
2.55.0.1082.g2b9226bbc0-goog