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

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Message-Id: <20240131162533.247710-5-mathieu.desnoyers@efficios.com>
Date: Wed, 31 Jan 2024 11:25:33 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Dan Williams <dan.j.williams@...el.com>,
	Arnd Bergmann <arnd@...db.de>,
	Dave Chinner <david@...morbit.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,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Matthew Wilcox <willy@...radead.org>,
	Russell King <linux@...linux.org.uk>,
	nvdimm@...ts.linux.dev,
	linux-cxl@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	dm-devel@...ts.linux.dev
Subject: [RFC PATCH v3 4/4] dax: Fix incorrect list of data cache 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 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@...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
Cc: dm-devel@...ts.linux.dev
---
 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