[RFC PATCH for 4.21 05/16] mm: Provide is_vma_noncached

Provide is_vma_noncached() static inline to allow generic code to
check whether the given vma consists of noncached memory.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: "Paul E. McKenney" <redacted>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Paul Turner <redacted>
CC: Thomas Gleixner <redacted>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Andi Kleen <redacted>
CC: Dave Watson <redacted>
CC: Chris Lameter <redacted>
CC: Ingo Molnar <mingo@redhat.com>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Ben Maurer <redacted>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Russell King <redacted>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Will Deacon <redacted>
CC: Michael Kerrisk <redacted>
CC: Boqun Feng <redacted>
CC: linux-mm@kvack.org
---
 include/linux/mm.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0416a7204be3..18acf4f339f8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -2551,6 +2551,30 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
 	return follow_page_mask(vma, address, foll_flags, &unused_page_mask);
 }
 
+static inline bool pgprot_same(pgprot_t a, pgprot_t b)
+{
+	return pgprot_val(a) == pgprot_val(b);
+}
+
+#ifdef pgprot_noncached
+static inline bool is_vma_noncached(struct vm_area_struct *vma)
+{
+	pgprot_t pgprot = vma->vm_page_prot;
+
+	/* Check whether architecture implements noncached pages. */
+	if (pgprot_same(pgprot_noncached(PAGE_KERNEL), PAGE_KERNEL))
+		return false;
+	if (!pgprot_same(pgprot, pgprot_noncached(pgprot)))
+		return false;
+	return true;
+}
+#else
+static inline bool is_vma_noncached(struct vm_area_struct *vma)
+{
+	return false;
+}
+#endif
+
 #define FOLL_WRITE	0x01	/* check pte is writable */
 #define FOLL_TOUCH	0x02	/* mark page accessed */
 #define FOLL_GET	0x04	/* do get_page on page */

-- 
2.11.0