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Date:   Mon, 13 May 2019 13:32:28 -0400 (EDT)
From:   Pankaj Gupta <pagupta@redhat.com>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     cohuck@redhat.com, Jan Kara <jack@suse.cz>,
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Subject: Re: [Qemu-devel] [PATCH v8 3/6] libnvdimm: add dax_dev sync flag
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Hi Dan,

While testing device mapper with DAX, I faced a bug with the commit:

commit ad428cdb525a97d15c0349fdc80f3d58befb50df
Author: Dan Williams <dan.j.williams@intel.com>
Date:   Wed Feb 20 21:12:50 2019 -0800

When I reverted the condition to old code[1] 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.

[1]

-               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 == MEMORY_DEVICE_FS_DAX
+                               && 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) == PHYS_PFN(__pa(end_kaddr)))
                        dax_enabled = true;
                put_dev_pagemap(pgmap);

Thanks,
Pankaj