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

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Message-Id: <20240130165255.212591-9-mathieu.desnoyers@efficios.com>
Date: Tue, 30 Jan 2024 11:52:55 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Dan Williams <dan.j.williams@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>
Cc: linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-mm@...ck.org,
	linux-arch@...r.kernel.org,
	Matthew Wilcox <willy@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	Russell King <linux@...linux.org.uk>,
	nvdimm@...ts.linux.dev,
	linux-cxl@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: [RFC PATCH v2 8/8] dax: Fix incorrect list of dcache aliasing architectures

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@...icios.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-mm@...ck.org
Cc: linux-arch@...r.kernel.org
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Vishal Verma <vishal.l.verma@...el.com>
Cc: Dave Jiang <dave.jiang@...el.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Russell King <linux@...linux.org.uk>
Cc: nvdimm@...ts.linux.dev
Cc: linux-cxl@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org
---
 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