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

[Dan Williams]

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@xxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> Cc: linux-arch@xxxxxxxxxxxxxxx
> Cc: linux-cxl@xxxxxxxxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-xfs@xxxxxxxxxxxxxxx
> Cc: dm-devel@xxxxxxxxxxxxxxx
> Cc: nvdimm@xxxxxxxxxxxxxxx
> ---
>  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@xxxxxxxxx>