dax: check for data cache aliasing at runtime

Replace the following fs/Kconfig:FS_DAX dependency:

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

By a runtime check within alloc_dax(). This runtime check returns
ERR_PTR(-EOPNOTSUPP) if the @ops parameter is non-NULL (which means
the kernel is using an aliased mapping) on an architecture which
has data cache aliasing.

Change the return value from NULL to PTR_ERR(-EOPNOTSUPP) for
CONFIG_DAX=n for consistency.

This is done in preparation for using cpu_dcache_is_aliasing() in a
following change which will properly support architectures which detect
data cache aliasing at runtime.

Link: https://lkml.kernel.org/r/20240215144633.96437-8-mathieu.desnoyers@efficios.com
Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Michael Sclafani <dm-devel@lists.linux.dev>
Cc: Mike Snitzer <snitzer@kernel.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 97ef2a9d878d12e8f1ea9e61d629e1af0b7d3e0c..7643b1a078d9f174a8e4ab25e0f3ac3de61ea47a 100644 (file)
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -451,6 +451,16 @@ struct dax_device *alloc_dax(void *private, const struct dax_operations *ops)
        dev_t devt;
        int minor;
 
+       /*
+        * Unavailable on architectures with virtually aliased data caches,
+        * except for device-dax (NULL operations pointer), which does
+        * not use aliased mappings from the kernel.
+        */
+       if (ops && (IS_ENABLED(CONFIG_ARM) ||
+           IS_ENABLED(CONFIG_MIPS) ||
+           IS_ENABLED(CONFIG_SPARC)))
+               return ERR_PTR(-EOPNOTSUPP);
+
        if (WARN_ON_ONCE(ops && !ops->zero_page_range))
                return ERR_PTR(-EINVAL);
 

diff --git a/fs/Kconfig b/fs/Kconfig
index 89fdbefd1075f8f5a071987bca3b4a50f687a887..713c8655fa0a6d3d5c4e8b0135a2ccbfb2d3f657 100644 (file)
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -60,7 +60,6 @@ endif # BLOCK
 config FS_DAX
        bool "File system based Direct Access (DAX) support"
        depends on MMU
-       depends on !(ARM || MIPS || SPARC)
        depends on ZONE_DEVICE || FS_DAX_LIMITED
        select FS_IOMAP
        select DAX