RE: [PATCH v4 08/12] dax: Fix incorrect list of data cache aliasing architectures

Dan Williams
2024-02-08T21:53:02Z

Mathieu Desnoyers wrote:
> 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);

Looks good,

Reviewed-by: Dan Williams <dan.j.williams@intel.com>