On Mon, May 13, 2019 at 10:32 AM Pankaj Gupta <pagupta(a)redhat.com> wrote:
While testing device mapper with DAX, I faced a bug with the commit:
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), will
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 == pgmap
+ && pfn_t_to_pfn(pfn) == PHYS_PFN(__pa(kaddr))
+ && 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.
We need to get that fixed up, but I don't see it as a blocker /
pre-requisite for virtio-pmem.