[RFC PATCH v2 8/8] dax: Fix incorrect list of dcache aliasing architectures

[Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>]

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 dcache.

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 dcache
aliasing, and therefore should work fine with FS_DAX.

This was turned into the following implementation of dax_is_supported()
by a preparatory change:

        return !IS_ENABLED(CONFIG_ARM) &&
               !IS_ENABLED(CONFIG_MIPS) &&
               !IS_ENABLED(CONFIG_SPARC);

Use dcache_is_aliasing() instead to figure out whether the environment
has aliasing dcaches.

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
---
 include/linux/dax.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/linux/dax.h b/include/linux/dax.h
index cfc8cd4a3eae..f59e604662e4 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -5,6 +5,7 @@
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/radix-tree.h>
+#include <linux/cacheinfo.h>
 
 typedef unsigned long dax_entry_t;
 
@@ -80,9 +81,7 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
 }
 static inline bool dax_is_supported(void)
 {
-	return !IS_ENABLED(CONFIG_ARM) &&
-	       !IS_ENABLED(CONFIG_MIPS) &&
-	       !IS_ENABLED(CONFIG_SPARC);
+	return !dcache_is_aliasing();
 }
 #else
 static inline void *dax_holder(struct dax_device *dax_dev)
-- 
2.39.2