Dave Chinner wrote:
> 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 <mathieu.desnoyers@xxxxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Cc: linux-mm@xxxxxxxxx
> > Cc: linux-arch@xxxxxxxxxxxxxxx
> > 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: nvdimm@xxxxxxxxxxxxxxx
> > Cc: linux-cxl@xxxxxxxxxxxxxxx
> > Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> > ---
> > 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.
Oh, good catch. Yes, I agree this can definitely be pushed down, but
then I think it should be pushed down all the way to make alloc_dax()
fail. That will need some additional fixups like:
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 8dcabf84d866..a35e60e62440 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2126,12 +2126,12 @@ static struct mapped_device *alloc_dev(int minor)
md->dax_dev = alloc_dax(md, &dm_dax_ops);
if (IS_ERR(md->dax_dev)) {
md->dax_dev = NULL;
- goto bad;
+ } else {
+ set_dax_nocache(md->dax_dev);
+ set_dax_nomc(md->dax_dev);
+ if (dax_add_host(md->dax_dev, md->disk))
+ goto bad;
}
- set_dax_nocache(md->dax_dev);
- set_dax_nomc(md->dax_dev);
- if (dax_add_host(md->dax_dev, md->disk))
- goto bad;
}
format_dev_t(md->name, MKDEV(_major, minor));
...to make it not fatal to fail to register the dax_dev.
