Re: [PATCH] dax: Fix last_page check in __bdev_dax_supported()

[Dan Williams]

On Wed, May 15, 2019 at 10:55 PM Vaibhav Jain <vaibhav@xxxxxxxxxxxxx> wrote:
>
> Presently __bdev_dax_supported() checks if first sector of last
> page ( last_page ) on the block device is aligned to page
> boundary. However the code to compute 'last_page' assumes that there
> are 8 sectors/page assuming a 4K page-size.
>
> This assumption breaks on architectures which use a different page
> size specifically PPC64 where page-size == 64K. Hence a warning is
> seen while trying to mount a xfs/ext4 file-system with dax enabled:
>
> $ sudo mount -o dax /dev/pmem0 /mnt/pmem
> XFS (pmem0): DAX enabled. Warning: EXPERIMENTAL, use at your own risk
> XFS (pmem0): DAX unsupported by block device. Turning off DAX.
>
> The patch fixes this issue by updating calculation of 'last_var' to
> take into account number-of-sectors/page instead of assuming it to be
> '8'.

Yes, I noticed this too and fixed it up in a wider change that also
allows device-mapper to validate each component device. Does this
patch work for you?

https://lore.kernel.org/lkml/155789172402.748145.11853718580748830476.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/