Use dax_is_supported() to validate whether the architecture has
virtually aliased data caches at mount time. Print an error and disable
DAX 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 <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: [email protected]
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Dan Williams <[email protected]>
Cc: Vishal Verma <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Russell King <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
 fs/ext2/super.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 01f9addc8b1f..30ff57d47ed4 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -955,7 +955,11 @@ static int ext2_fill_super(struct super_block *sb, void 
*data, int silent)
        blocksize = BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
 
        if (test_opt(sb, DAX)) {
-               if (!sbi->s_daxdev) {
+               if (!dax_is_supported()) {
+                       ext2_msg(sb, KERN_ERR,
+                               "DAX unsupported by architecture. Turning off 
DAX.");
+                       clear_opt(sbi->s_mount_opt, DAX);
+               } else if (!sbi->s_daxdev) {
                        ext2_msg(sb, KERN_ERR,
                                "DAX unsupported by block device. Turning off 
DAX.");
                        clear_opt(sbi->s_mount_opt, DAX);
-- 
2.39.2


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