[RFC PATCH v2 4/8] ext4: Use dax_is_supported()

[Mathieu Desnoyers]

Use dax_is_supported() to validate whether the architecture has
virtually aliased data caches at mount time. Mount fails if dax=always
is requested as a mount option on an architecture which does not support
DAX.

This is relevant for architectures which require a dynamic check
to validate whether they have virtually aliased data caches.

Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Cc: linux-ext4@xxxxxxxxxxxxxxx
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: nvdimm@xxxxxxxxxxxxxxx
Cc: linux-cxl@xxxxxxxxxxxxxxx
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
 fs/ext4/super.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index c5fcf377ab1f..f2c11ae3ec29 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4743,7 +4743,10 @@ static int ext4_check_feature_compatibility(struct super_block *sb,
 	}
 
 	if (sbi->s_mount_opt & EXT4_MOUNT_DAX_ALWAYS) {
-		if (ext4_has_feature_inline_data(sb)) {
+		if (!dax_is_supported()) {
+			ext4_msg(sb, KERN_ERR, "DAX unsupported by architecture.");
+			return -EINVAL;
+		} else if (ext4_has_feature_inline_data(sb)) {
 			ext4_msg(sb, KERN_ERR, "Cannot use DAX on a filesystem"
 					" that may contain inline data");
 			return -EINVAL;
-- 
2.39.2