[RFC PATCH v2 2/8] erofs: Use dax_is_supported()

[Mathieu Desnoyers]

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 <mathieu.desnoyers at efficios.com>
Cc: Gao Xiang <xiang at kernel.org>
Cc: Chao Yu <chao at kernel.org>
Cc: Yue Hu <huyue2 at coolpad.com>
Cc: Jeffle Xu <jefflexu at linux.alibaba.com>
Cc: linux-erofs at lists.ozlabs.org
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: linux-mm at kvack.org
Cc: linux-arch at vger.kernel.org
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Vishal Verma <vishal.l.verma at intel.com>
Cc: Dave Jiang <dave.jiang at intel.com>
Cc: Matthew Wilcox <willy at infradead.org>
Cc: Arnd Bergmann <arnd at arndb.de>
Cc: Russell King <linux at armlinux.org.uk>
Cc: nvdimm at lists.linux.dev
Cc: linux-cxl at vger.kernel.org
Cc: linux-fsdevel at vger.kernel.org
---
 fs/erofs/super.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 3789d6224513..82e569bd5889 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -644,7 +644,10 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 	}
 
 	if (test_opt(&sbi->opt, DAX_ALWAYS)) {
-		if (!sbi->dax_dev) {
+		if (!dax_is_supported()) {
+			errorfc(fc, "DAX unsupported by architecture. Turning off DAX.");
+			clear_opt(&sbi->opt, DAX_ALWAYS);
+		} else if (!sbi->dax_dev) {
 			errorfc(fc, "DAX unsupported by block device. Turning off DAX.");
 			clear_opt(&sbi->opt, DAX_ALWAYS);
 		} else if (sbi->blkszbits != PAGE_SHIFT) {
-- 
2.39.2