On Tue, Jan 30, 2024 at 11:52:55AM -0500, 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 dcache.
>
> This is a regression introduced in the v5.13 Linux kernel where the
> dax mount option is removed for 32-bit ARMv7 boards which have no dcache
> aliasing, and therefore should work fine with FS_DAX.
>
> This was turned into the following implementation of dax_is_supported()
> by a preparatory change:
>
> return !IS_ENABLED(CONFIG_ARM) &&
> !IS_ENABLED(CONFIG_MIPS) &&
> !IS_ENABLED(CONFIG_SPARC);
>
> Use dcache_is_aliasing() instead to figure out whether the environment
> has aliasing dcaches.
>
> Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing
> caches")
> Signed-off-by: Mathieu Desnoyers <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Linus Torvalds <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: Dan Williams <[email protected]>
> Cc: Vishal Verma <[email protected]>
> Cc: Dave Jiang <[email protected]>
> Cc: Matthew Wilcox <[email protected]>
> Cc: Arnd Bergmann <[email protected]>
> Cc: Russell King <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> ---
> include/linux/dax.h | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index cfc8cd4a3eae..f59e604662e4 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -5,6 +5,7 @@
> #include <linux/fs.h>
> #include <linux/mm.h>
> #include <linux/radix-tree.h>
> +#include <linux/cacheinfo.h>
>
> typedef unsigned long dax_entry_t;
>
> @@ -80,9 +81,7 @@ static inline bool daxdev_mapping_supported(struct
> vm_area_struct *vma,
> }
> static inline bool dax_is_supported(void)
> {
> - return !IS_ENABLED(CONFIG_ARM) &&
> - !IS_ENABLED(CONFIG_MIPS) &&
> - !IS_ENABLED(CONFIG_SPARC);
> + return !dcache_is_aliasing();
Yeah, if this is just a one liner should go into
fs_dax_get_by_bdev(), similar to the blk_queue_dax() check at the
start of the function.
I also noticed that device mapper uses fs_dax_get_by_bdev() to
determine if it can support DAX, but this patch set does not address
that case. Hence it really seems to me like fs_dax_get_by_bdev() is
the right place to put this check.
-Dave.
--
Dave Chinner
[email protected]
