[RFC PATCH v3 4/4] dax: Fix incorrect list of data cache aliasing architectures

[Mathieu Desnoyers]

commit d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
prevents DAX from building on architectures with virtually aliased
dcache with:

  depends on !(ARM || MIPS || SPARC)

This check is too broad (e.g. recent ARMv7 don't have virtually aliased
dcaches), and also misses many other architectures with virtually
aliased data cache.

This is a regression introduced in the v5.13 Linux kernel where the
dax mount option is removed for 32-bit ARMv7 boards which have no data
cache aliasing, and therefore should work fine with FS_DAX.

This was turned into the following check in alloc_dax() by a preparatory
change:

        if (IS_ENABLED(CONFIG_ARM) ||
            IS_ENABLED(CONFIG_MIPS) ||
            IS_ENABLED(CONFIG_SPARC))
                return NULL;

Use cpu_dcache_is_aliasing() instead to figure out whether the environment
has aliasing data caches.

Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
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
Cc: dm-devel@xxxxxxxxxxxxxxx
---
 drivers/dax/super.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index e9f397b8a5a3..8c3a6e8e6334 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -13,6 +13,7 @@
 #include <linux/uio.h>
 #include <linux/dax.h>
 #include <linux/fs.h>
+#include <linux/cacheinfo.h>
 #include "dax-private.h"
 
 /**
@@ -446,9 +447,7 @@ struct dax_device *alloc_dax(void *private, const struct dax_operations *ops)
 	int minor;
 
 	/* Unavailable on architectures with virtually aliased data caches. */
-	if (IS_ENABLED(CONFIG_ARM) ||
-	    IS_ENABLED(CONFIG_MIPS) ||
-	    IS_ENABLED(CONFIG_SPARC))
+	if (cpu_dcache_is_aliasing())
 		return NULL;
 
 	if (WARN_ON_ONCE(ops && !ops->zero_page_range))
-- 
2.39.2