> Hi Dan,
> While testing device mapper with DAX, I faced a bug with the commit:
> commit ad428cdb525a97d15c0349fdc80f3d58befb50df
> Author: Dan Williams <dan.j.williams(a)intel.com>
> Date: Wed Feb 20 21:12:50 2019 -0800
> When I reverted the condition to old code it worked for me. I
> am thinking when we map two different devices (e.g with device mapper),
> start & end pfn still point to same pgmap? Or there is something else which
> I am missing here.
> Note: I tested only EXT4.
> - if (pgmap && pgmap->type == MEMORY_DEVICE_FS_DAX)
> + end_pgmap = get_dev_pagemap(pfn_t_to_pfn(end_pfn), NULL);
> + if (pgmap && pgmap == end_pgmap && pgmap->type
> + && pfn_t_to_page(pfn)->pgmap == pgmap
> + && pfn_t_to_page(end_pfn)->pgmap ==
> + && pfn_t_to_pfn(pfn) ==
> + && pfn_t_to_pfn(end_pfn) ==
Ugh, yes, device-mapper continues to be an awkward fit for dax (or
vice versa). We would either need a way to have a multi-level pfn to
pagemap lookup for composite devices, or a way to discern that even
though the pagemap is different that the result is still valid / not
an indication that we have leaked into an unassociated address range.
Perhaps a per-daxdev callback for ->dax_supported() so that
device-mapper internals can be used for this validation.
Yes, Will look at it.
We need to get that fixed up, but I don't see it as a blocker /
pre-requisite for virtio-pmem.
Agree. Will send virtio-pmem patch series.