linux-kernel - Re: [Qemu-devel] [RFC v2 1/2] virtio: add pmem driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1499190564.23017177.1524762938762.JavaMail.zimbra@redhat.com>
Date:   Thu, 26 Apr 2018 13:15:38 -0400 (EDT)
From:   Pankaj Gupta <pagupta@...hat.com>
To:     Jeff Moyer <jmoyer@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Jan Kara <jack@...e.cz>, KVM list <kvm@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        linux-nvdimm <linux-nvdimm@...1.01.org>,
        Ross Zwisler <ross.zwisler@...el.com>,
        Qemu Developers <qemu-devel@...gnu.org>,
        lcapitulino@...hat.com, Linux MM <linux-mm@...ck.org>,
        niteshnarayanlal@...mail.com,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Marcel Apfelbaum <marcel@...hat.com>,
        Nitesh Narayan Lal <nilal@...hat.com>,
        Haozhong Zhang <haozhong.zhang@...el.com>,
        Rik van Riel <riel@...riel.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Kevin Wolf <kwolf@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Igor Mammedov <imammedo@...hat.com>
Subject: Re: [Qemu-devel] [RFC v2 1/2] virtio: add pmem driver


> 
> Dan Williams <dan.j.williams@...el.com> writes:
> 
> > [ adding Jeff directly since he has also been looking at
> > infrastructure to track when MAP_SYNC should be disabled ]
> >
> > On Wed, Apr 25, 2018 at 7:21 AM, Dan Williams <dan.j.williams@...el.com>
> > wrote:
> >> On Wed, Apr 25, 2018 at 4:24 AM, Pankaj Gupta <pagupta@...hat.com> wrote:
> >>> This patch adds virtio-pmem driver for KVM
> >>> guest.
> >>
> >> Minor nit, please expand your changelog line wrapping to 72 columns.
> >>
> >>>
> >>> Guest reads the persistent memory range
> >>> information from Qemu over VIRTIO and registers
> >>> it on nvdimm_bus. It also creates a nd_region
> >>> object with the persistent memory range
> >>> information so that existing 'nvdimm/pmem'
> >>> driver can reserve this into system memory map.
> >>> This way 'virtio-pmem' driver uses existing
> >>> functionality of pmem driver to register persistent
> >>> memory compatible for DAX capable filesystems.
> >>
> >> We need some additional enabling to disable MAP_SYNC for this
> 
> enable to disable... I like it!  ;-)
> 
> >> configuration. In other words, if fsync() is required then we must
> >> disable the MAP_SYNC optimization. I think this should be a struct
> >> dax_device property looked up at mmap time in each MAP_SYNC capable
> >> ->mmap() file operation implementation.

I understand you mean we want to disable 'MAP_SYNC' optimization as
we are relying on additional fsync. You mean if we add a property/flag
in dax_device struct and its set, disable 'MAP_SYNC' accordingly during
mmap time for corresponding filesystems?  

> 
> Ideally, qemu (seabios?) would advertise a platform capabilities
> sub-table that doesn't fill in the flush bits.

Could you please elaborate on this, how its related to disabling
MAP_SYNC? We are not doing entire nvdimm device emulation. 

> 
> -Jeff
> 
>