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

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Date: Thu, 8 Feb 2024 13:52:53 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 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>, Vishal Verma
	<vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, Matthew Wilcox
	<willy@...radead.org>, Russell King <linux@...linux.org.uk>,
	<linux-arch@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
	<linux-fsdevel@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-xfs@...r.kernel.org>, <dm-devel@...ts.linux.dev>,
	<nvdimm@...ts.linux.dev>, <linux-s390@...r.kernel.org>
Subject: RE: [PATCH v4 08/12] dax: Fix incorrect list of data cache aliasing
 architectures

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@...icios.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.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: linux-arch@...r.kernel.org
> Cc: linux-cxl@...r.kernel.org
> Cc: linux-fsdevel@...r.kernel.org
> Cc: linux-mm@...ck.org
> Cc: linux-xfs@...r.kernel.org
> Cc: dm-devel@...ts.linux.dev
> Cc: nvdimm@...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 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@...el.com>