On Mon, May 13, 2019 at 10:32 AM Pankaj Gupta <pagupta@xxxxxxxxxx> wrote: > > > Hi Dan, > > While testing device mapper with DAX, I faced a bug with the commit: > > commit ad428cdb525a97d15c0349fdc80f3d58befb50df > Author: Dan Williams <dan.j.williams@xxxxxxxxx> > 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))) 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.
