>From a3bfac5e1582d9c31e67090b306efedf7c392d36 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Tue, 2 Oct 2018 11:58:22 +0200
Subject: [PATCH] proc: Show DAX mappings as having VM_MIXEDMAP flag

Until commit e1fb4a08649 "dax: remove VM_MIXEDMAP for fsdax and device
dax", userspace could distinguish DAX and non-DAX mappings in
/proc/<pid>/smaps by checking whether the VMA has VM_MIXEDMAP (mm in
smaps) flag. And indeed some applications started doing this. Maintain
backwards compatibility by faking VM_MIXEDMAP flag in smaps for DAX
mappings.

Fixes: e1fb4a0864958fac2fb1b23f9f4562a9f90e3e8f
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/proc/task_mmu.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 5ea1d64cb0b4..9cd8e84610a7 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -19,6 +19,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/uaccess.h>
 #include <linux/pkeys.h>
+#include <linux/fs.h>
 
 #include <asm/elf.h>
 #include <asm/tlb.h>
@@ -654,12 +655,18 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 #endif /* CONFIG_ARCH_HAS_PKEYS */
 	};
 	size_t i;
+	unsigned long flags = vma->vm_flags;
 
+	/*
+	 * We fake VM_MIXEDMAP for DAX mappings here as some apps depend on it.
+	 */
+	if (vma_is_dax(vma))
+		flags |= VM_MIXEDMAP;
 	seq_puts(m, "VmFlags: ");
 	for (i = 0; i < BITS_PER_LONG; i++) {
 		if (!mnemonics[i][0])
 			continue;
-		if (vma->vm_flags & (1UL << i)) {
+		if (flags & (1UL << i)) {
 			seq_putc(m, mnemonics[i][0]);
 			seq_putc(m, mnemonics[i][1]);
 			seq_putc(m, ' ');
-- 
2.16.4