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    Subject[PATCH v4 08/12] dax: Fix incorrect list of data cache aliasing architectures
    Date
    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 v4.0 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 (ops && (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@efficios.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    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: linux-arch@vger.kernel.org
    Cc: linux-cxl@vger.kernel.org
    Cc: linux-fsdevel@vger.kernel.org
    Cc: linux-mm@kvack.org
    Cc: linux-xfs@vger.kernel.org
    Cc: dm-devel@lists.linux.dev
    Cc: nvdimm@lists.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 ce5bffa86bba..a21a7c262382 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"

    /**
    @@ -455,9 +456,7 @@ struct dax_device *alloc_dax(void *private, const struct dax_operations *ops)
    * 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)))
    + if (ops && cpu_dcache_is_aliasing())
    return ERR_PTR(-EOPNOTSUPP);

    if (WARN_ON_ONCE(ops && !ops->zero_page_range))
    --
    2.39.2

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