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Date: Tue, 14 May 2019 01:27:17 -0400 (EDT) From: Pankaj Gupta <pagupta@...hat.com> To: Dan Williams <dan.j.williams@...el.com> Cc: Jan Kara <jack@...e.cz>, KVM list <kvm@...r.kernel.org>, "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, david <david@...morbit.com>, Qemu Developers <qemu-devel@...gnu.org>, virtualization@...ts.linux-foundation.org, Andreas Dilger <adilger.kernel@...ger.ca>, Ross Zwisler <zwisler@...nel.org>, Andrea Arcangeli <aarcange@...hat.com>, Dave Jiang <dave.jiang@...el.com>, jstaron@...gle.com, linux-nvdimm <linux-nvdimm@...ts.01.org>, Vishal L Verma <vishal.l.verma@...el.com>, David Hildenbrand <david@...hat.com>, Matthew Wilcox <willy@...radead.org>, Christoph Hellwig <hch@...radead.org>, Linux ACPI <linux-acpi@...r.kernel.org>, jmoyer <jmoyer@...hat.com>, linux-ext4 <linux-ext4@...r.kernel.org>, Len Brown <lenb@...nel.org>, Adam Borowski <kilobyte@...band.pl>, Rik van Riel <riel@...riel.com>, yuval shaia <yuval.shaia@...cle.com>, Stefan Hajnoczi <stefanha@...hat.com>, Igor Mammedov <imammedo@...hat.com>, lcapitulino@...hat.com, Kevin Wolf <kwolf@...hat.com>, Nitesh Narayan Lal <nilal@...hat.com>, Theodore Ts'o <tytso@....edu>, Xiao Guangrong <xiaoguangrong.eric@...il.com>, cohuck@...hat.com, "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-xfs <linux-xfs@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>, "Darrick J. Wong" <darrick.wong@...cle.com> Subject: Re: [Qemu-devel] [PATCH v8 3/6] libnvdimm: add dax_dev sync flag > > > > > > Hi Dan, > > > > While testing device mapper with DAX, I faced a bug with the commit: > > > > commit ad428cdb525a97d15c0349fdc80f3d58befb50df > > Author: Dan Williams <dan.j.williams@...el.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))) > > 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. Thank you, Pankaj > >
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